LCOV - code coverage report
Current view: top level - src/bin/pg_rewind - xlogreader.c (source / functions) Hit Total Coverage
Test: PostgreSQL 17devel Lines: 377 722 52.2 %
Date: 2023-12-11 16:10:55 Functions: 19 28 67.9 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * xlogreader.c
       4             :  *      Generic XLog reading facility
       5             :  *
       6             :  * Portions Copyright (c) 2013-2023, PostgreSQL Global Development Group
       7             :  *
       8             :  * IDENTIFICATION
       9             :  *      src/backend/access/transam/xlogreader.c
      10             :  *
      11             :  * NOTES
      12             :  *      See xlogreader.h for more notes on this facility.
      13             :  *
      14             :  *      This file is compiled as both front-end and backend code, so it
      15             :  *      may not use ereport, server-defined static variables, etc.
      16             :  *-------------------------------------------------------------------------
      17             :  */
      18             : #include "postgres.h"
      19             : 
      20             : #include <unistd.h>
      21             : #ifdef USE_LZ4
      22             : #include <lz4.h>
      23             : #endif
      24             : #ifdef USE_ZSTD
      25             : #include <zstd.h>
      26             : #endif
      27             : 
      28             : #include "access/transam.h"
      29             : #include "access/xlog_internal.h"
      30             : #include "access/xlogreader.h"
      31             : #include "access/xlogrecord.h"
      32             : #include "catalog/pg_control.h"
      33             : #include "common/pg_lzcompress.h"
      34             : #include "replication/origin.h"
      35             : 
      36             : #ifndef FRONTEND
      37             : #include "miscadmin.h"
      38             : #include "pgstat.h"
      39             : #include "utils/memutils.h"
      40             : #else
      41             : #include "common/logging.h"
      42             : #endif
      43             : 
      44             : static void report_invalid_record(XLogReaderState *state, const char *fmt,...)
      45             :             pg_attribute_printf(2, 3);
      46             : static void allocate_recordbuf(XLogReaderState *state, uint32 reclength);
      47             : static int  ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr,
      48             :                              int reqLen);
      49             : static void XLogReaderInvalReadState(XLogReaderState *state);
      50             : static XLogPageReadResult XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking);
      51             : static bool ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
      52             :                                   XLogRecPtr PrevRecPtr, XLogRecord *record, bool randAccess);
      53             : static bool ValidXLogRecord(XLogReaderState *state, XLogRecord *record,
      54             :                             XLogRecPtr recptr);
      55             : static void ResetDecoder(XLogReaderState *state);
      56             : static void WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt,
      57             :                                int segsize, const char *waldir);
      58             : 
      59             : /* size of the buffer allocated for error message. */
      60             : #define MAX_ERRORMSG_LEN 1000
      61             : 
      62             : /*
      63             :  * Default size; large enough that typical users of XLogReader won't often need
      64             :  * to use the 'oversized' memory allocation code path.
      65             :  */
      66             : #define DEFAULT_DECODE_BUFFER_SIZE (64 * 1024)
      67             : 
      68             : /*
      69             :  * Construct a string in state->errormsg_buf explaining what's wrong with
      70             :  * the current record being read.
      71             :  */
      72             : static void
      73           0 : report_invalid_record(XLogReaderState *state, const char *fmt,...)
      74             : {
      75             :     va_list     args;
      76             : 
      77           0 :     fmt = _(fmt);
      78             : 
      79           0 :     va_start(args, fmt);
      80           0 :     vsnprintf(state->errormsg_buf, MAX_ERRORMSG_LEN, fmt, args);
      81           0 :     va_end(args);
      82             : 
      83           0 :     state->errormsg_deferred = true;
      84           0 : }
      85             : 
      86             : /*
      87             :  * Set the size of the decoding buffer.  A pointer to a caller supplied memory
      88             :  * region may also be passed in, in which case non-oversized records will be
      89             :  * decoded there.
      90             :  */
      91             : void
      92           0 : XLogReaderSetDecodeBuffer(XLogReaderState *state, void *buffer, size_t size)
      93             : {
      94             :     Assert(state->decode_buffer == NULL);
      95             : 
      96           0 :     state->decode_buffer = buffer;
      97           0 :     state->decode_buffer_size = size;
      98           0 :     state->decode_buffer_tail = buffer;
      99           0 :     state->decode_buffer_head = buffer;
     100           0 : }
     101             : 
     102             : /*
     103             :  * Allocate and initialize a new XLogReader.
     104             :  *
     105             :  * Returns NULL if the xlogreader couldn't be allocated.
     106             :  */
     107             : XLogReaderState *
     108          78 : XLogReaderAllocate(int wal_segment_size, const char *waldir,
     109             :                    XLogReaderRoutine *routine, void *private_data)
     110             : {
     111             :     XLogReaderState *state;
     112             : 
     113             :     state = (XLogReaderState *)
     114          78 :         palloc_extended(sizeof(XLogReaderState),
     115             :                         MCXT_ALLOC_NO_OOM | MCXT_ALLOC_ZERO);
     116          78 :     if (!state)
     117           0 :         return NULL;
     118             : 
     119             :     /* initialize caller-provided support functions */
     120          78 :     state->routine = *routine;
     121             : 
     122             :     /*
     123             :      * Permanently allocate readBuf.  We do it this way, rather than just
     124             :      * making a static array, for two reasons: (1) no need to waste the
     125             :      * storage in most instantiations of the backend; (2) a static char array
     126             :      * isn't guaranteed to have any particular alignment, whereas
     127             :      * palloc_extended() will provide MAXALIGN'd storage.
     128             :      */
     129          78 :     state->readBuf = (char *) palloc_extended(XLOG_BLCKSZ,
     130             :                                               MCXT_ALLOC_NO_OOM);
     131          78 :     if (!state->readBuf)
     132             :     {
     133           0 :         pfree(state);
     134           0 :         return NULL;
     135             :     }
     136             : 
     137             :     /* Initialize segment info. */
     138          78 :     WALOpenSegmentInit(&state->seg, &state->segcxt, wal_segment_size,
     139             :                        waldir);
     140             : 
     141             :     /* system_identifier initialized to zeroes above */
     142          78 :     state->private_data = private_data;
     143             :     /* ReadRecPtr, EndRecPtr and readLen initialized to zeroes above */
     144          78 :     state->errormsg_buf = palloc_extended(MAX_ERRORMSG_LEN + 1,
     145             :                                           MCXT_ALLOC_NO_OOM);
     146          78 :     if (!state->errormsg_buf)
     147             :     {
     148           0 :         pfree(state->readBuf);
     149           0 :         pfree(state);
     150           0 :         return NULL;
     151             :     }
     152          78 :     state->errormsg_buf[0] = '\0';
     153             : 
     154             :     /*
     155             :      * Allocate an initial readRecordBuf of minimal size, which can later be
     156             :      * enlarged if necessary.
     157             :      */
     158          78 :     allocate_recordbuf(state, 0);
     159          78 :     return state;
     160             : }
     161             : 
     162             : void
     163          78 : XLogReaderFree(XLogReaderState *state)
     164             : {
     165          78 :     if (state->seg.ws_file != -1)
     166           0 :         state->routine.segment_close(state);
     167             : 
     168          78 :     if (state->decode_buffer && state->free_decode_buffer)
     169          78 :         pfree(state->decode_buffer);
     170             : 
     171          78 :     pfree(state->errormsg_buf);
     172          78 :     if (state->readRecordBuf)
     173          78 :         pfree(state->readRecordBuf);
     174          78 :     pfree(state->readBuf);
     175          78 :     pfree(state);
     176          78 : }
     177             : 
     178             : /*
     179             :  * Allocate readRecordBuf to fit a record of at least the given length.
     180             :  *
     181             :  * readRecordBufSize is set to the new buffer size.
     182             :  *
     183             :  * To avoid useless small increases, round its size to a multiple of
     184             :  * XLOG_BLCKSZ, and make sure it's at least 5*Max(BLCKSZ, XLOG_BLCKSZ) to start
     185             :  * with.  (That is enough for all "normal" records, but very large commit or
     186             :  * abort records might need more space.)
     187             :  *
     188             :  * Note: This routine should *never* be called for xl_tot_len until the header
     189             :  * of the record has been fully validated.
     190             :  */
     191             : static void
     192          78 : allocate_recordbuf(XLogReaderState *state, uint32 reclength)
     193             : {
     194          78 :     uint32      newSize = reclength;
     195             : 
     196          78 :     newSize += XLOG_BLCKSZ - (newSize % XLOG_BLCKSZ);
     197          78 :     newSize = Max(newSize, 5 * Max(BLCKSZ, XLOG_BLCKSZ));
     198             : 
     199          78 :     if (state->readRecordBuf)
     200           0 :         pfree(state->readRecordBuf);
     201          78 :     state->readRecordBuf = (char *) palloc(newSize);
     202          78 :     state->readRecordBufSize = newSize;
     203          78 : }
     204             : 
     205             : /*
     206             :  * Initialize the passed segment structs.
     207             :  */
     208             : static void
     209          78 : WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt,
     210             :                    int segsize, const char *waldir)
     211             : {
     212          78 :     seg->ws_file = -1;
     213          78 :     seg->ws_segno = 0;
     214          78 :     seg->ws_tli = 0;
     215             : 
     216          78 :     segcxt->ws_segsize = segsize;
     217          78 :     if (waldir)
     218          78 :         snprintf(segcxt->ws_dir, MAXPGPATH, "%s", waldir);
     219          78 : }
     220             : 
     221             : /*
     222             :  * Begin reading WAL at 'RecPtr'.
     223             :  *
     224             :  * 'RecPtr' should point to the beginning of a valid WAL record.  Pointing at
     225             :  * the beginning of a page is also OK, if there is a new record right after
     226             :  * the page header, i.e. not a continuation.
     227             :  *
     228             :  * This does not make any attempt to read the WAL yet, and hence cannot fail.
     229             :  * If the starting address is not correct, the first call to XLogReadRecord()
     230             :  * will error out.
     231             :  */
     232             : void
     233        5200 : XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr)
     234             : {
     235             :     Assert(!XLogRecPtrIsInvalid(RecPtr));
     236             : 
     237        5200 :     ResetDecoder(state);
     238             : 
     239             :     /* Begin at the passed-in record pointer. */
     240        5200 :     state->EndRecPtr = RecPtr;
     241        5200 :     state->NextRecPtr = RecPtr;
     242        5200 :     state->ReadRecPtr = InvalidXLogRecPtr;
     243        5200 :     state->DecodeRecPtr = InvalidXLogRecPtr;
     244        5200 : }
     245             : 
     246             : /*
     247             :  * Release the last record that was returned by XLogNextRecord(), if any, to
     248             :  * free up space.  Returns the LSN past the end of the record.
     249             :  */
     250             : XLogRecPtr
     251      357088 : XLogReleasePreviousRecord(XLogReaderState *state)
     252             : {
     253             :     DecodedXLogRecord *record;
     254             :     XLogRecPtr  next_lsn;
     255             : 
     256      357088 :     if (!state->record)
     257      183744 :         return InvalidXLogRecPtr;
     258             : 
     259             :     /*
     260             :      * Remove it from the decoded record queue.  It must be the oldest item
     261             :      * decoded, decode_queue_head.
     262             :      */
     263      173344 :     record = state->record;
     264      173344 :     next_lsn = record->next_lsn;
     265             :     Assert(record == state->decode_queue_head);
     266      173344 :     state->record = NULL;
     267      173344 :     state->decode_queue_head = record->next;
     268             : 
     269             :     /* It might also be the newest item decoded, decode_queue_tail. */
     270      173344 :     if (state->decode_queue_tail == record)
     271      173344 :         state->decode_queue_tail = NULL;
     272             : 
     273             :     /* Release the space. */
     274      173344 :     if (unlikely(record->oversized))
     275             :     {
     276             :         /* It's not in the decode buffer, so free it to release space. */
     277           0 :         pfree(record);
     278             :     }
     279             :     else
     280             :     {
     281             :         /* It must be the head (oldest) record in the decode buffer. */
     282             :         Assert(state->decode_buffer_head == (char *) record);
     283             : 
     284             :         /*
     285             :          * We need to update head to point to the next record that is in the
     286             :          * decode buffer, if any, being careful to skip oversized ones
     287             :          * (they're not in the decode buffer).
     288             :          */
     289      173344 :         record = record->next;
     290      173344 :         while (unlikely(record && record->oversized))
     291           0 :             record = record->next;
     292             : 
     293      173344 :         if (record)
     294             :         {
     295             :             /* Adjust head to release space up to the next record. */
     296           0 :             state->decode_buffer_head = (char *) record;
     297             :         }
     298             :         else
     299             :         {
     300             :             /*
     301             :              * Otherwise we might as well just reset head and tail to the
     302             :              * start of the buffer space, because we're empty.  This means
     303             :              * we'll keep overwriting the same piece of memory if we're not
     304             :              * doing any prefetching.
     305             :              */
     306      173344 :             state->decode_buffer_head = state->decode_buffer;
     307      173344 :             state->decode_buffer_tail = state->decode_buffer;
     308             :         }
     309             :     }
     310             : 
     311      173344 :     return next_lsn;
     312             : }
     313             : 
     314             : /*
     315             :  * Attempt to read an XLOG record.
     316             :  *
     317             :  * XLogBeginRead() or XLogFindNextRecord() and then XLogReadAhead() must be
     318             :  * called before the first call to XLogNextRecord().  This functions returns
     319             :  * records and errors that were put into an internal queue by XLogReadAhead().
     320             :  *
     321             :  * On success, a record is returned.
     322             :  *
     323             :  * The returned record (or *errormsg) points to an internal buffer that's
     324             :  * valid until the next call to XLogNextRecord.
     325             :  */
     326             : DecodedXLogRecord *
     327      178544 : XLogNextRecord(XLogReaderState *state, char **errormsg)
     328             : {
     329             :     /* Release the last record returned by XLogNextRecord(). */
     330      178544 :     XLogReleasePreviousRecord(state);
     331             : 
     332      178544 :     if (state->decode_queue_head == NULL)
     333             :     {
     334           0 :         *errormsg = NULL;
     335           0 :         if (state->errormsg_deferred)
     336             :         {
     337           0 :             if (state->errormsg_buf[0] != '\0')
     338           0 :                 *errormsg = state->errormsg_buf;
     339           0 :             state->errormsg_deferred = false;
     340             :         }
     341             : 
     342             :         /*
     343             :          * state->EndRecPtr is expected to have been set by the last call to
     344             :          * XLogBeginRead() or XLogNextRecord(), and is the location of the
     345             :          * error.
     346             :          */
     347             :         Assert(!XLogRecPtrIsInvalid(state->EndRecPtr));
     348             : 
     349           0 :         return NULL;
     350             :     }
     351             : 
     352             :     /*
     353             :      * Record this as the most recent record returned, so that we'll release
     354             :      * it next time.  This also exposes it to the traditional
     355             :      * XLogRecXXX(xlogreader) macros, which work with the decoder rather than
     356             :      * the record for historical reasons.
     357             :      */
     358      178544 :     state->record = state->decode_queue_head;
     359             : 
     360             :     /*
     361             :      * Update the pointers to the beginning and one-past-the-end of this
     362             :      * record, again for the benefit of historical code that expected the
     363             :      * decoder to track this rather than accessing these fields of the record
     364             :      * itself.
     365             :      */
     366      178544 :     state->ReadRecPtr = state->record->lsn;
     367      178544 :     state->EndRecPtr = state->record->next_lsn;
     368             : 
     369      178544 :     *errormsg = NULL;
     370             : 
     371      178544 :     return state->record;
     372             : }
     373             : 
     374             : /*
     375             :  * Attempt to read an XLOG record.
     376             :  *
     377             :  * XLogBeginRead() or XLogFindNextRecord() must be called before the first call
     378             :  * to XLogReadRecord().
     379             :  *
     380             :  * If the page_read callback fails to read the requested data, NULL is
     381             :  * returned.  The callback is expected to have reported the error; errormsg
     382             :  * is set to NULL.
     383             :  *
     384             :  * If the reading fails for some other reason, NULL is also returned, and
     385             :  * *errormsg is set to a string with details of the failure.
     386             :  *
     387             :  * The returned pointer (or *errormsg) points to an internal buffer that's
     388             :  * valid until the next call to XLogReadRecord.
     389             :  */
     390             : XLogRecord *
     391      178544 : XLogReadRecord(XLogReaderState *state, char **errormsg)
     392             : {
     393             :     DecodedXLogRecord *decoded;
     394             : 
     395             :     /*
     396             :      * Release last returned record, if there is one.  We need to do this so
     397             :      * that we can check for empty decode queue accurately.
     398             :      */
     399      178544 :     XLogReleasePreviousRecord(state);
     400             : 
     401             :     /*
     402             :      * Call XLogReadAhead() in blocking mode to make sure there is something
     403             :      * in the queue, though we don't use the result.
     404             :      */
     405      178544 :     if (!XLogReaderHasQueuedRecordOrError(state))
     406      178544 :         XLogReadAhead(state, false /* nonblocking */ );
     407             : 
     408             :     /* Consume the head record or error. */
     409      178544 :     decoded = XLogNextRecord(state, errormsg);
     410      178544 :     if (decoded)
     411             :     {
     412             :         /*
     413             :          * This function returns a pointer to the record's header, not the
     414             :          * actual decoded record.  The caller will access the decoded record
     415             :          * through the XLogRecGetXXX() macros, which reach the decoded
     416             :          * recorded as xlogreader->record.
     417             :          */
     418             :         Assert(state->record == decoded);
     419      178544 :         return &decoded->header;
     420             :     }
     421             : 
     422           0 :     return NULL;
     423             : }
     424             : 
     425             : /*
     426             :  * Allocate space for a decoded record.  The only member of the returned
     427             :  * object that is initialized is the 'oversized' flag, indicating that the
     428             :  * decoded record wouldn't fit in the decode buffer and must eventually be
     429             :  * freed explicitly.
     430             :  *
     431             :  * The caller is responsible for adjusting decode_buffer_tail with the real
     432             :  * size after successfully decoding a record into this space.  This way, if
     433             :  * decoding fails, then there is nothing to undo unless the 'oversized' flag
     434             :  * was set and pfree() must be called.
     435             :  *
     436             :  * Return NULL if there is no space in the decode buffer and allow_oversized
     437             :  * is false, or if memory allocation fails for an oversized buffer.
     438             :  */
     439             : static DecodedXLogRecord *
     440      178544 : XLogReadRecordAlloc(XLogReaderState *state, size_t xl_tot_len, bool allow_oversized)
     441             : {
     442      178544 :     size_t      required_space = DecodeXLogRecordRequiredSpace(xl_tot_len);
     443      178544 :     DecodedXLogRecord *decoded = NULL;
     444             : 
     445             :     /* Allocate a circular decode buffer if we don't have one already. */
     446      178544 :     if (unlikely(state->decode_buffer == NULL))
     447             :     {
     448          78 :         if (state->decode_buffer_size == 0)
     449          78 :             state->decode_buffer_size = DEFAULT_DECODE_BUFFER_SIZE;
     450          78 :         state->decode_buffer = palloc(state->decode_buffer_size);
     451          78 :         state->decode_buffer_head = state->decode_buffer;
     452          78 :         state->decode_buffer_tail = state->decode_buffer;
     453          78 :         state->free_decode_buffer = true;
     454             :     }
     455             : 
     456             :     /* Try to allocate space in the circular decode buffer. */
     457      178544 :     if (state->decode_buffer_tail >= state->decode_buffer_head)
     458             :     {
     459             :         /* Empty, or tail is to the right of head. */
     460      178544 :         if (required_space <=
     461      178544 :             state->decode_buffer_size -
     462      178544 :             (state->decode_buffer_tail - state->decode_buffer))
     463             :         {
     464             :             /*-
     465             :              * There is space between tail and end.
     466             :              *
     467             :              * +-----+--------------------+-----+
     468             :              * |     |////////////////////|here!|
     469             :              * +-----+--------------------+-----+
     470             :              *       ^                    ^
     471             :              *       |                    |
     472             :              *       h                    t
     473             :              */
     474      178544 :             decoded = (DecodedXLogRecord *) state->decode_buffer_tail;
     475      178544 :             decoded->oversized = false;
     476      178544 :             return decoded;
     477             :         }
     478           0 :         else if (required_space <
     479           0 :                  state->decode_buffer_head - state->decode_buffer)
     480             :         {
     481             :             /*-
     482             :              * There is space between start and head.
     483             :              *
     484             :              * +-----+--------------------+-----+
     485             :              * |here!|////////////////////|     |
     486             :              * +-----+--------------------+-----+
     487             :              *       ^                    ^
     488             :              *       |                    |
     489             :              *       h                    t
     490             :              */
     491           0 :             decoded = (DecodedXLogRecord *) state->decode_buffer;
     492           0 :             decoded->oversized = false;
     493           0 :             return decoded;
     494             :         }
     495             :     }
     496             :     else
     497             :     {
     498             :         /* Tail is to the left of head. */
     499           0 :         if (required_space <
     500           0 :             state->decode_buffer_head - state->decode_buffer_tail)
     501             :         {
     502             :             /*-
     503             :              * There is space between tail and head.
     504             :              *
     505             :              * +-----+--------------------+-----+
     506             :              * |/////|here!               |/////|
     507             :              * +-----+--------------------+-----+
     508             :              *       ^                    ^
     509             :              *       |                    |
     510             :              *       t                    h
     511             :              */
     512           0 :             decoded = (DecodedXLogRecord *) state->decode_buffer_tail;
     513           0 :             decoded->oversized = false;
     514           0 :             return decoded;
     515             :         }
     516             :     }
     517             : 
     518             :     /* Not enough space in the decode buffer.  Are we allowed to allocate? */
     519           0 :     if (allow_oversized)
     520             :     {
     521           0 :         decoded = palloc(required_space);
     522           0 :         decoded->oversized = true;
     523           0 :         return decoded;
     524             :     }
     525             : 
     526           0 :     return NULL;
     527             : }
     528             : 
     529             : static XLogPageReadResult
     530      178544 : XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking)
     531             : {
     532             :     XLogRecPtr  RecPtr;
     533             :     XLogRecord *record;
     534             :     XLogRecPtr  targetPagePtr;
     535             :     bool        randAccess;
     536             :     uint32      len,
     537             :                 total_len;
     538             :     uint32      targetRecOff;
     539             :     uint32      pageHeaderSize;
     540             :     bool        assembled;
     541             :     bool        gotheader;
     542             :     int         readOff;
     543             :     DecodedXLogRecord *decoded;
     544             :     char       *errormsg;       /* not used */
     545             : 
     546             :     /*
     547             :      * randAccess indicates whether to verify the previous-record pointer of
     548             :      * the record we're reading.  We only do this if we're reading
     549             :      * sequentially, which is what we initially assume.
     550             :      */
     551      178544 :     randAccess = false;
     552             : 
     553             :     /* reset error state */
     554      178544 :     state->errormsg_buf[0] = '\0';
     555      178544 :     decoded = NULL;
     556             : 
     557      178544 :     state->abortedRecPtr = InvalidXLogRecPtr;
     558      178544 :     state->missingContrecPtr = InvalidXLogRecPtr;
     559             : 
     560      178544 :     RecPtr = state->NextRecPtr;
     561             : 
     562      178544 :     if (state->DecodeRecPtr != InvalidXLogRecPtr)
     563             :     {
     564             :         /* read the record after the one we just read */
     565             : 
     566             :         /*
     567             :          * NextRecPtr is pointing to end+1 of the previous WAL record.  If
     568             :          * we're at a page boundary, no more records can fit on the current
     569             :          * page. We must skip over the page header, but we can't do that until
     570             :          * we've read in the page, since the header size is variable.
     571             :          */
     572             :     }
     573             :     else
     574             :     {
     575             :         /*
     576             :          * Caller supplied a position to start at.
     577             :          *
     578             :          * In this case, NextRecPtr should already be pointing either to a
     579             :          * valid record starting position or alternatively to the beginning of
     580             :          * a page. See the header comments for XLogBeginRead.
     581             :          */
     582             :         Assert(RecPtr % XLOG_BLCKSZ == 0 || XRecOffIsValid(RecPtr));
     583        5200 :         randAccess = true;
     584             :     }
     585             : 
     586      178544 : restart:
     587      178544 :     state->nonblocking = nonblocking;
     588      178544 :     state->currRecPtr = RecPtr;
     589      178544 :     assembled = false;
     590             : 
     591      178544 :     targetPagePtr = RecPtr - (RecPtr % XLOG_BLCKSZ);
     592      178544 :     targetRecOff = RecPtr % XLOG_BLCKSZ;
     593             : 
     594             :     /*
     595             :      * Read the page containing the record into state->readBuf. Request enough
     596             :      * byte to cover the whole record header, or at least the part of it that
     597             :      * fits on the same page.
     598             :      */
     599      178544 :     readOff = ReadPageInternal(state, targetPagePtr,
     600      178544 :                                Min(targetRecOff + SizeOfXLogRecord, XLOG_BLCKSZ));
     601      178544 :     if (readOff == XLREAD_WOULDBLOCK)
     602           0 :         return XLREAD_WOULDBLOCK;
     603      178544 :     else if (readOff < 0)
     604           0 :         goto err;
     605             : 
     606             :     /*
     607             :      * ReadPageInternal always returns at least the page header, so we can
     608             :      * examine it now.
     609             :      */
     610      178544 :     pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) state->readBuf);
     611      178544 :     if (targetRecOff == 0)
     612             :     {
     613             :         /*
     614             :          * At page start, so skip over page header.
     615             :          */
     616         196 :         RecPtr += pageHeaderSize;
     617         196 :         targetRecOff = pageHeaderSize;
     618             :     }
     619      178348 :     else if (targetRecOff < pageHeaderSize)
     620             :     {
     621           0 :         report_invalid_record(state, "invalid record offset at %X/%X: expected at least %u, got %u",
     622           0 :                               LSN_FORMAT_ARGS(RecPtr),
     623             :                               pageHeaderSize, targetRecOff);
     624           0 :         goto err;
     625             :     }
     626             : 
     627      178544 :     if ((((XLogPageHeader) state->readBuf)->xlp_info & XLP_FIRST_IS_CONTRECORD) &&
     628             :         targetRecOff == pageHeaderSize)
     629             :     {
     630           0 :         report_invalid_record(state, "contrecord is requested by %X/%X",
     631           0 :                               LSN_FORMAT_ARGS(RecPtr));
     632           0 :         goto err;
     633             :     }
     634             : 
     635             :     /* ReadPageInternal has verified the page header */
     636             :     Assert(pageHeaderSize <= readOff);
     637             : 
     638             :     /*
     639             :      * Read the record length.
     640             :      *
     641             :      * NB: Even though we use an XLogRecord pointer here, the whole record
     642             :      * header might not fit on this page. xl_tot_len is the first field of the
     643             :      * struct, so it must be on this page (the records are MAXALIGNed), but we
     644             :      * cannot access any other fields until we've verified that we got the
     645             :      * whole header.
     646             :      */
     647      178544 :     record = (XLogRecord *) (state->readBuf + RecPtr % XLOG_BLCKSZ);
     648      178544 :     total_len = record->xl_tot_len;
     649             : 
     650             :     /*
     651             :      * If the whole record header is on this page, validate it immediately.
     652             :      * Otherwise do just a basic sanity check on xl_tot_len, and validate the
     653             :      * rest of the header after reading it from the next page.  The xl_tot_len
     654             :      * check is necessary here to ensure that we enter the "Need to reassemble
     655             :      * record" code path below; otherwise we might fail to apply
     656             :      * ValidXLogRecordHeader at all.
     657             :      */
     658      178544 :     if (targetRecOff <= XLOG_BLCKSZ - SizeOfXLogRecord)
     659             :     {
     660      178220 :         if (!ValidXLogRecordHeader(state, RecPtr, state->DecodeRecPtr, record,
     661             :                                    randAccess))
     662           0 :             goto err;
     663      178220 :         gotheader = true;
     664             :     }
     665             :     else
     666             :     {
     667             :         /* There may be no next page if it's too small. */
     668         324 :         if (total_len < SizeOfXLogRecord)
     669             :         {
     670           0 :             report_invalid_record(state,
     671             :                                   "invalid record length at %X/%X: expected at least %u, got %u",
     672           0 :                                   LSN_FORMAT_ARGS(RecPtr),
     673             :                                   (uint32) SizeOfXLogRecord, total_len);
     674           0 :             goto err;
     675             :         }
     676             :         /* We'll validate the header once we have the next page. */
     677         324 :         gotheader = false;
     678             :     }
     679             : 
     680             :     /*
     681             :      * Try to find space to decode this record, if we can do so without
     682             :      * calling palloc.  If we can't, we'll try again below after we've
     683             :      * validated that total_len isn't garbage bytes from a recycled WAL page.
     684             :      */
     685      178544 :     decoded = XLogReadRecordAlloc(state,
     686             :                                   total_len,
     687             :                                   false /* allow_oversized */ );
     688      178544 :     if (decoded == NULL && nonblocking)
     689             :     {
     690             :         /*
     691             :          * There is no space in the circular decode buffer, and the caller is
     692             :          * only reading ahead.  The caller should consume existing records to
     693             :          * make space.
     694             :          */
     695           0 :         return XLREAD_WOULDBLOCK;
     696             :     }
     697             : 
     698      178544 :     len = XLOG_BLCKSZ - RecPtr % XLOG_BLCKSZ;
     699      178544 :     if (total_len > len)
     700             :     {
     701             :         /* Need to reassemble record */
     702             :         char       *contdata;
     703             :         XLogPageHeader pageHeader;
     704             :         char       *buffer;
     705             :         uint32      gotlen;
     706             : 
     707        8604 :         assembled = true;
     708             : 
     709             :         /*
     710             :          * We always have space for a couple of pages, enough to validate a
     711             :          * boundary-spanning record header.
     712             :          */
     713             :         Assert(state->readRecordBufSize >= XLOG_BLCKSZ * 2);
     714             :         Assert(state->readRecordBufSize >= len);
     715             : 
     716             :         /* Copy the first fragment of the record from the first page. */
     717        8604 :         memcpy(state->readRecordBuf,
     718        8604 :                state->readBuf + RecPtr % XLOG_BLCKSZ, len);
     719        8604 :         buffer = state->readRecordBuf + len;
     720        8604 :         gotlen = len;
     721             : 
     722             :         do
     723             :         {
     724             :             /* Calculate pointer to beginning of next page */
     725        8608 :             targetPagePtr += XLOG_BLCKSZ;
     726             : 
     727             :             /* Wait for the next page to become available */
     728        8608 :             readOff = ReadPageInternal(state, targetPagePtr,
     729        8608 :                                        Min(total_len - gotlen + SizeOfXLogShortPHD,
     730             :                                            XLOG_BLCKSZ));
     731             : 
     732        8608 :             if (readOff == XLREAD_WOULDBLOCK)
     733           0 :                 return XLREAD_WOULDBLOCK;
     734        8608 :             else if (readOff < 0)
     735           0 :                 goto err;
     736             : 
     737             :             Assert(SizeOfXLogShortPHD <= readOff);
     738             : 
     739        8608 :             pageHeader = (XLogPageHeader) state->readBuf;
     740             : 
     741             :             /*
     742             :              * If we were expecting a continuation record and got an
     743             :              * "overwrite contrecord" flag, that means the continuation record
     744             :              * was overwritten with a different record.  Restart the read by
     745             :              * assuming the address to read is the location where we found
     746             :              * this flag; but keep track of the LSN of the record we were
     747             :              * reading, for later verification.
     748             :              */
     749        8608 :             if (pageHeader->xlp_info & XLP_FIRST_IS_OVERWRITE_CONTRECORD)
     750             :             {
     751           0 :                 state->overwrittenRecPtr = RecPtr;
     752           0 :                 RecPtr = targetPagePtr;
     753           0 :                 goto restart;
     754             :             }
     755             : 
     756             :             /* Check that the continuation on next page looks valid */
     757        8608 :             if (!(pageHeader->xlp_info & XLP_FIRST_IS_CONTRECORD))
     758             :             {
     759           0 :                 report_invalid_record(state,
     760             :                                       "there is no contrecord flag at %X/%X",
     761           0 :                                       LSN_FORMAT_ARGS(RecPtr));
     762           0 :                 goto err;
     763             :             }
     764             : 
     765             :             /*
     766             :              * Cross-check that xlp_rem_len agrees with how much of the record
     767             :              * we expect there to be left.
     768             :              */
     769        8608 :             if (pageHeader->xlp_rem_len == 0 ||
     770        8608 :                 total_len != (pageHeader->xlp_rem_len + gotlen))
     771             :             {
     772           0 :                 report_invalid_record(state,
     773             :                                       "invalid contrecord length %u (expected %lld) at %X/%X",
     774             :                                       pageHeader->xlp_rem_len,
     775           0 :                                       ((long long) total_len) - gotlen,
     776           0 :                                       LSN_FORMAT_ARGS(RecPtr));
     777           0 :                 goto err;
     778             :             }
     779             : 
     780             :             /* Append the continuation from this page to the buffer */
     781        8608 :             pageHeaderSize = XLogPageHeaderSize(pageHeader);
     782             : 
     783        8608 :             if (readOff < pageHeaderSize)
     784           0 :                 readOff = ReadPageInternal(state, targetPagePtr,
     785             :                                            pageHeaderSize);
     786             : 
     787             :             Assert(pageHeaderSize <= readOff);
     788             : 
     789        8608 :             contdata = (char *) state->readBuf + pageHeaderSize;
     790        8608 :             len = XLOG_BLCKSZ - pageHeaderSize;
     791        8608 :             if (pageHeader->xlp_rem_len < len)
     792        8604 :                 len = pageHeader->xlp_rem_len;
     793             : 
     794        8608 :             if (readOff < pageHeaderSize + len)
     795           0 :                 readOff = ReadPageInternal(state, targetPagePtr,
     796           0 :                                            pageHeaderSize + len);
     797             : 
     798        8608 :             memcpy(buffer, (char *) contdata, len);
     799        8608 :             buffer += len;
     800        8608 :             gotlen += len;
     801             : 
     802             :             /* If we just reassembled the record header, validate it. */
     803        8608 :             if (!gotheader)
     804             :             {
     805         324 :                 record = (XLogRecord *) state->readRecordBuf;
     806         324 :                 if (!ValidXLogRecordHeader(state, RecPtr, state->DecodeRecPtr,
     807             :                                            record, randAccess))
     808           0 :                     goto err;
     809         324 :                 gotheader = true;
     810             :             }
     811             : 
     812             :             /*
     813             :              * We might need a bigger buffer.  We have validated the record
     814             :              * header, in the case that it split over a page boundary.  We've
     815             :              * also cross-checked total_len against xlp_rem_len on the second
     816             :              * page, and verified xlp_pageaddr on both.
     817             :              */
     818        8608 :             if (total_len > state->readRecordBufSize)
     819             :             {
     820             :                 char        save_copy[XLOG_BLCKSZ * 2];
     821             : 
     822             :                 /*
     823             :                  * Save and restore the data we already had.  It can't be more
     824             :                  * than two pages.
     825             :                  */
     826             :                 Assert(gotlen <= lengthof(save_copy));
     827             :                 Assert(gotlen <= state->readRecordBufSize);
     828           0 :                 memcpy(save_copy, state->readRecordBuf, gotlen);
     829           0 :                 allocate_recordbuf(state, total_len);
     830           0 :                 memcpy(state->readRecordBuf, save_copy, gotlen);
     831           0 :                 buffer = state->readRecordBuf + gotlen;
     832             :             }
     833        8608 :         } while (gotlen < total_len);
     834             :         Assert(gotheader);
     835             : 
     836        8604 :         record = (XLogRecord *) state->readRecordBuf;
     837        8604 :         if (!ValidXLogRecord(state, record, RecPtr))
     838           0 :             goto err;
     839             : 
     840        8604 :         pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) state->readBuf);
     841        8604 :         state->DecodeRecPtr = RecPtr;
     842        8604 :         state->NextRecPtr = targetPagePtr + pageHeaderSize
     843        8604 :             + MAXALIGN(pageHeader->xlp_rem_len);
     844             :     }
     845             :     else
     846             :     {
     847             :         /* Wait for the record data to become available */
     848      169940 :         readOff = ReadPageInternal(state, targetPagePtr,
     849      169940 :                                    Min(targetRecOff + total_len, XLOG_BLCKSZ));
     850      169940 :         if (readOff == XLREAD_WOULDBLOCK)
     851           0 :             return XLREAD_WOULDBLOCK;
     852      169940 :         else if (readOff < 0)
     853           0 :             goto err;
     854             : 
     855             :         /* Record does not cross a page boundary */
     856      169940 :         if (!ValidXLogRecord(state, record, RecPtr))
     857           0 :             goto err;
     858             : 
     859      169940 :         state->NextRecPtr = RecPtr + MAXALIGN(total_len);
     860             : 
     861      169940 :         state->DecodeRecPtr = RecPtr;
     862             :     }
     863             : 
     864             :     /*
     865             :      * Special processing if it's an XLOG SWITCH record
     866             :      */
     867      178544 :     if (record->xl_rmid == RM_XLOG_ID &&
     868       12070 :         (record->xl_info & ~XLR_INFO_MASK) == XLOG_SWITCH)
     869             :     {
     870             :         /* Pretend it extends to end of segment */
     871          16 :         state->NextRecPtr += state->segcxt.ws_segsize - 1;
     872          16 :         state->NextRecPtr -= XLogSegmentOffset(state->NextRecPtr, state->segcxt.ws_segsize);
     873             :     }
     874             : 
     875             :     /*
     876             :      * If we got here without a DecodedXLogRecord, it means we needed to
     877             :      * validate total_len before trusting it, but by now we've done that.
     878             :      */
     879      178544 :     if (decoded == NULL)
     880             :     {
     881             :         Assert(!nonblocking);
     882           0 :         decoded = XLogReadRecordAlloc(state,
     883             :                                       total_len,
     884             :                                       true /* allow_oversized */ );
     885             :         /* allocation should always happen under allow_oversized */
     886             :         Assert(decoded != NULL);
     887             :     }
     888             : 
     889      178544 :     if (DecodeXLogRecord(state, decoded, record, RecPtr, &errormsg))
     890             :     {
     891             :         /* Record the location of the next record. */
     892      178544 :         decoded->next_lsn = state->NextRecPtr;
     893             : 
     894             :         /*
     895             :          * If it's in the decode buffer, mark the decode buffer space as
     896             :          * occupied.
     897             :          */
     898      178544 :         if (!decoded->oversized)
     899             :         {
     900             :             /* The new decode buffer head must be MAXALIGNed. */
     901             :             Assert(decoded->size == MAXALIGN(decoded->size));
     902      178544 :             if ((char *) decoded == state->decode_buffer)
     903      178544 :                 state->decode_buffer_tail = state->decode_buffer + decoded->size;
     904             :             else
     905           0 :                 state->decode_buffer_tail += decoded->size;
     906             :         }
     907             : 
     908             :         /* Insert it into the queue of decoded records. */
     909             :         Assert(state->decode_queue_tail != decoded);
     910      178544 :         if (state->decode_queue_tail)
     911           0 :             state->decode_queue_tail->next = decoded;
     912      178544 :         state->decode_queue_tail = decoded;
     913      178544 :         if (!state->decode_queue_head)
     914      178544 :             state->decode_queue_head = decoded;
     915      178544 :         return XLREAD_SUCCESS;
     916             :     }
     917             : 
     918           0 : err:
     919           0 :     if (assembled)
     920             :     {
     921             :         /*
     922             :          * We get here when a record that spans multiple pages needs to be
     923             :          * assembled, but something went wrong -- perhaps a contrecord piece
     924             :          * was lost.  If caller is WAL replay, it will know where the aborted
     925             :          * record was and where to direct followup WAL to be written, marking
     926             :          * the next piece with XLP_FIRST_IS_OVERWRITE_CONTRECORD, which will
     927             :          * in turn signal downstream WAL consumers that the broken WAL record
     928             :          * is to be ignored.
     929             :          */
     930           0 :         state->abortedRecPtr = RecPtr;
     931           0 :         state->missingContrecPtr = targetPagePtr;
     932             : 
     933             :         /*
     934             :          * If we got here without reporting an error, make sure an error is
     935             :          * queued so that XLogPrefetcherReadRecord() doesn't bring us back a
     936             :          * second time and clobber the above state.
     937             :          */
     938           0 :         state->errormsg_deferred = true;
     939             :     }
     940             : 
     941           0 :     if (decoded && decoded->oversized)
     942           0 :         pfree(decoded);
     943             : 
     944             :     /*
     945             :      * Invalidate the read state. We might read from a different source after
     946             :      * failure.
     947             :      */
     948           0 :     XLogReaderInvalReadState(state);
     949             : 
     950             :     /*
     951             :      * If an error was written to errmsg_buf, it'll be returned to the caller
     952             :      * of XLogReadRecord() after all successfully decoded records from the
     953             :      * read queue.
     954             :      */
     955             : 
     956           0 :     return XLREAD_FAIL;
     957             : }
     958             : 
     959             : /*
     960             :  * Try to decode the next available record, and return it.  The record will
     961             :  * also be returned to XLogNextRecord(), which must be called to 'consume'
     962             :  * each record.
     963             :  *
     964             :  * If nonblocking is true, may return NULL due to lack of data or WAL decoding
     965             :  * space.
     966             :  */
     967             : DecodedXLogRecord *
     968      178544 : XLogReadAhead(XLogReaderState *state, bool nonblocking)
     969             : {
     970             :     XLogPageReadResult result;
     971             : 
     972      178544 :     if (state->errormsg_deferred)
     973           0 :         return NULL;
     974             : 
     975      178544 :     result = XLogDecodeNextRecord(state, nonblocking);
     976      178544 :     if (result == XLREAD_SUCCESS)
     977             :     {
     978             :         Assert(state->decode_queue_tail != NULL);
     979      178544 :         return state->decode_queue_tail;
     980             :     }
     981             : 
     982           0 :     return NULL;
     983             : }
     984             : 
     985             : /*
     986             :  * Read a single xlog page including at least [pageptr, reqLen] of valid data
     987             :  * via the page_read() callback.
     988             :  *
     989             :  * Returns XLREAD_FAIL if the required page cannot be read for some
     990             :  * reason; errormsg_buf is set in that case (unless the error occurs in the
     991             :  * page_read callback).
     992             :  *
     993             :  * Returns XLREAD_WOULDBLOCK if the requested data can't be read without
     994             :  * waiting.  This can be returned only if the installed page_read callback
     995             :  * respects the state->nonblocking flag, and cannot read the requested data
     996             :  * immediately.
     997             :  *
     998             :  * We fetch the page from a reader-local cache if we know we have the required
     999             :  * data and if there hasn't been any error since caching the data.
    1000             :  */
    1001             : static int
    1002      357092 : ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
    1003             : {
    1004             :     int         readLen;
    1005             :     uint32      targetPageOff;
    1006             :     XLogSegNo   targetSegNo;
    1007             :     XLogPageHeader hdr;
    1008             : 
    1009             :     Assert((pageptr % XLOG_BLCKSZ) == 0);
    1010             : 
    1011      357092 :     XLByteToSeg(pageptr, targetSegNo, state->segcxt.ws_segsize);
    1012      357092 :     targetPageOff = XLogSegmentOffset(pageptr, state->segcxt.ws_segsize);
    1013             : 
    1014             :     /* check whether we have all the requested data already */
    1015      357092 :     if (targetSegNo == state->seg.ws_segno &&
    1016      356998 :         targetPageOff == state->segoff && reqLen <= state->readLen)
    1017      345620 :         return state->readLen;
    1018             : 
    1019             :     /*
    1020             :      * Invalidate contents of internal buffer before read attempt.  Just set
    1021             :      * the length to 0, rather than a full XLogReaderInvalReadState(), so we
    1022             :      * don't forget the segment we last successfully read.
    1023             :      */
    1024       11472 :     state->readLen = 0;
    1025             : 
    1026             :     /*
    1027             :      * Data is not in our buffer.
    1028             :      *
    1029             :      * Every time we actually read the segment, even if we looked at parts of
    1030             :      * it before, we need to do verification as the page_read callback might
    1031             :      * now be rereading data from a different source.
    1032             :      *
    1033             :      * Whenever switching to a new WAL segment, we read the first page of the
    1034             :      * file and validate its header, even if that's not where the target
    1035             :      * record is.  This is so that we can check the additional identification
    1036             :      * info that is present in the first page's "long" header.
    1037             :      */
    1038       11472 :     if (targetSegNo != state->seg.ws_segno && targetPageOff != 0)
    1039             :     {
    1040          46 :         XLogRecPtr  targetSegmentPtr = pageptr - targetPageOff;
    1041             : 
    1042          46 :         readLen = state->routine.page_read(state, targetSegmentPtr, XLOG_BLCKSZ,
    1043             :                                            state->currRecPtr,
    1044             :                                            state->readBuf);
    1045          46 :         if (readLen == XLREAD_WOULDBLOCK)
    1046           0 :             return XLREAD_WOULDBLOCK;
    1047          46 :         else if (readLen < 0)
    1048           0 :             goto err;
    1049             : 
    1050             :         /* we can be sure to have enough WAL available, we scrolled back */
    1051             :         Assert(readLen == XLOG_BLCKSZ);
    1052             : 
    1053          46 :         if (!XLogReaderValidatePageHeader(state, targetSegmentPtr,
    1054             :                                           state->readBuf))
    1055           0 :             goto err;
    1056             :     }
    1057             : 
    1058             :     /*
    1059             :      * First, read the requested data length, but at least a short page header
    1060             :      * so that we can validate it.
    1061             :      */
    1062       11472 :     readLen = state->routine.page_read(state, pageptr, Max(reqLen, SizeOfXLogShortPHD),
    1063             :                                        state->currRecPtr,
    1064             :                                        state->readBuf);
    1065       11472 :     if (readLen == XLREAD_WOULDBLOCK)
    1066           0 :         return XLREAD_WOULDBLOCK;
    1067       11472 :     else if (readLen < 0)
    1068           0 :         goto err;
    1069             : 
    1070             :     Assert(readLen <= XLOG_BLCKSZ);
    1071             : 
    1072             :     /* Do we have enough data to check the header length? */
    1073       11472 :     if (readLen <= SizeOfXLogShortPHD)
    1074           0 :         goto err;
    1075             : 
    1076             :     Assert(readLen >= reqLen);
    1077             : 
    1078       11472 :     hdr = (XLogPageHeader) state->readBuf;
    1079             : 
    1080             :     /* still not enough */
    1081       11472 :     if (readLen < XLogPageHeaderSize(hdr))
    1082             :     {
    1083           0 :         readLen = state->routine.page_read(state, pageptr, XLogPageHeaderSize(hdr),
    1084             :                                            state->currRecPtr,
    1085             :                                            state->readBuf);
    1086           0 :         if (readLen == XLREAD_WOULDBLOCK)
    1087           0 :             return XLREAD_WOULDBLOCK;
    1088           0 :         else if (readLen < 0)
    1089           0 :             goto err;
    1090             :     }
    1091             : 
    1092             :     /*
    1093             :      * Now that we know we have the full header, validate it.
    1094             :      */
    1095       11472 :     if (!XLogReaderValidatePageHeader(state, pageptr, (char *) hdr))
    1096           0 :         goto err;
    1097             : 
    1098             :     /* update read state information */
    1099       11472 :     state->seg.ws_segno = targetSegNo;
    1100       11472 :     state->segoff = targetPageOff;
    1101       11472 :     state->readLen = readLen;
    1102             : 
    1103       11472 :     return readLen;
    1104             : 
    1105           0 : err:
    1106           0 :     XLogReaderInvalReadState(state);
    1107             : 
    1108           0 :     return XLREAD_FAIL;
    1109             : }
    1110             : 
    1111             : /*
    1112             :  * Invalidate the xlogreader's read state to force a re-read.
    1113             :  */
    1114             : static void
    1115           0 : XLogReaderInvalReadState(XLogReaderState *state)
    1116             : {
    1117           0 :     state->seg.ws_segno = 0;
    1118           0 :     state->segoff = 0;
    1119           0 :     state->readLen = 0;
    1120           0 : }
    1121             : 
    1122             : /*
    1123             :  * Validate an XLOG record header.
    1124             :  *
    1125             :  * This is just a convenience subroutine to avoid duplicated code in
    1126             :  * XLogReadRecord.  It's not intended for use from anywhere else.
    1127             :  */
    1128             : static bool
    1129      178544 : ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
    1130             :                       XLogRecPtr PrevRecPtr, XLogRecord *record,
    1131             :                       bool randAccess)
    1132             : {
    1133      178544 :     if (record->xl_tot_len < SizeOfXLogRecord)
    1134             :     {
    1135           0 :         report_invalid_record(state,
    1136             :                               "invalid record length at %X/%X: expected at least %u, got %u",
    1137           0 :                               LSN_FORMAT_ARGS(RecPtr),
    1138             :                               (uint32) SizeOfXLogRecord, record->xl_tot_len);
    1139           0 :         return false;
    1140             :     }
    1141      178544 :     if (!RmgrIdIsValid(record->xl_rmid))
    1142             :     {
    1143           0 :         report_invalid_record(state,
    1144             :                               "invalid resource manager ID %u at %X/%X",
    1145           0 :                               record->xl_rmid, LSN_FORMAT_ARGS(RecPtr));
    1146           0 :         return false;
    1147             :     }
    1148      178544 :     if (randAccess)
    1149             :     {
    1150             :         /*
    1151             :          * We can't exactly verify the prev-link, but surely it should be less
    1152             :          * than the record's own address.
    1153             :          */
    1154        5200 :         if (!(record->xl_prev < RecPtr))
    1155             :         {
    1156           0 :             report_invalid_record(state,
    1157             :                                   "record with incorrect prev-link %X/%X at %X/%X",
    1158           0 :                                   LSN_FORMAT_ARGS(record->xl_prev),
    1159           0 :                                   LSN_FORMAT_ARGS(RecPtr));
    1160           0 :             return false;
    1161             :         }
    1162             :     }
    1163             :     else
    1164             :     {
    1165             :         /*
    1166             :          * Record's prev-link should exactly match our previous location. This
    1167             :          * check guards against torn WAL pages where a stale but valid-looking
    1168             :          * WAL record starts on a sector boundary.
    1169             :          */
    1170      173344 :         if (record->xl_prev != PrevRecPtr)
    1171             :         {
    1172           0 :             report_invalid_record(state,
    1173             :                                   "record with incorrect prev-link %X/%X at %X/%X",
    1174           0 :                                   LSN_FORMAT_ARGS(record->xl_prev),
    1175           0 :                                   LSN_FORMAT_ARGS(RecPtr));
    1176           0 :             return false;
    1177             :         }
    1178             :     }
    1179             : 
    1180      178544 :     return true;
    1181             : }
    1182             : 
    1183             : 
    1184             : /*
    1185             :  * CRC-check an XLOG record.  We do not believe the contents of an XLOG
    1186             :  * record (other than to the minimal extent of computing the amount of
    1187             :  * data to read in) until we've checked the CRCs.
    1188             :  *
    1189             :  * We assume all of the record (that is, xl_tot_len bytes) has been read
    1190             :  * into memory at *record.  Also, ValidXLogRecordHeader() has accepted the
    1191             :  * record's header, which means in particular that xl_tot_len is at least
    1192             :  * SizeOfXLogRecord.
    1193             :  */
    1194             : static bool
    1195      178544 : ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
    1196             : {
    1197             :     pg_crc32c   crc;
    1198             : 
    1199             :     Assert(record->xl_tot_len >= SizeOfXLogRecord);
    1200             : 
    1201             :     /* Calculate the CRC */
    1202      178544 :     INIT_CRC32C(crc);
    1203      178544 :     COMP_CRC32C(crc, ((char *) record) + SizeOfXLogRecord, record->xl_tot_len - SizeOfXLogRecord);
    1204             :     /* include the record header last */
    1205      178544 :     COMP_CRC32C(crc, (char *) record, offsetof(XLogRecord, xl_crc));
    1206      178544 :     FIN_CRC32C(crc);
    1207             : 
    1208      178544 :     if (!EQ_CRC32C(record->xl_crc, crc))
    1209             :     {
    1210           0 :         report_invalid_record(state,
    1211             :                               "incorrect resource manager data checksum in record at %X/%X",
    1212           0 :                               LSN_FORMAT_ARGS(recptr));
    1213           0 :         return false;
    1214             :     }
    1215             : 
    1216      178544 :     return true;
    1217             : }
    1218             : 
    1219             : /*
    1220             :  * Validate a page header.
    1221             :  *
    1222             :  * Check if 'phdr' is valid as the header of the XLog page at position
    1223             :  * 'recptr'.
    1224             :  */
    1225             : bool
    1226       11518 : XLogReaderValidatePageHeader(XLogReaderState *state, XLogRecPtr recptr,
    1227             :                              char *phdr)
    1228             : {
    1229             :     XLogSegNo   segno;
    1230             :     int32       offset;
    1231       11518 :     XLogPageHeader hdr = (XLogPageHeader) phdr;
    1232             : 
    1233             :     Assert((recptr % XLOG_BLCKSZ) == 0);
    1234             : 
    1235       11518 :     XLByteToSeg(recptr, segno, state->segcxt.ws_segsize);
    1236       11518 :     offset = XLogSegmentOffset(recptr, state->segcxt.ws_segsize);
    1237             : 
    1238       11518 :     if (hdr->xlp_magic != XLOG_PAGE_MAGIC)
    1239             :     {
    1240             :         char        fname[MAXFNAMELEN];
    1241             : 
    1242           0 :         XLogFileName(fname, state->seg.ws_tli, segno, state->segcxt.ws_segsize);
    1243             : 
    1244           0 :         report_invalid_record(state,
    1245             :                               "invalid magic number %04X in WAL segment %s, LSN %X/%X, offset %u",
    1246           0 :                               hdr->xlp_magic,
    1247             :                               fname,
    1248           0 :                               LSN_FORMAT_ARGS(recptr),
    1249             :                               offset);
    1250           0 :         return false;
    1251             :     }
    1252             : 
    1253       11518 :     if ((hdr->xlp_info & ~XLP_ALL_FLAGS) != 0)
    1254             :     {
    1255             :         char        fname[MAXFNAMELEN];
    1256             : 
    1257           0 :         XLogFileName(fname, state->seg.ws_tli, segno, state->segcxt.ws_segsize);
    1258             : 
    1259           0 :         report_invalid_record(state,
    1260             :                               "invalid info bits %04X in WAL segment %s, LSN %X/%X, offset %u",
    1261           0 :                               hdr->xlp_info,
    1262             :                               fname,
    1263           0 :                               LSN_FORMAT_ARGS(recptr),
    1264             :                               offset);
    1265           0 :         return false;
    1266             :     }
    1267             : 
    1268       11518 :     if (hdr->xlp_info & XLP_LONG_HEADER)
    1269             :     {
    1270         112 :         XLogLongPageHeader longhdr = (XLogLongPageHeader) hdr;
    1271             : 
    1272         112 :         if (state->system_identifier &&
    1273           0 :             longhdr->xlp_sysid != state->system_identifier)
    1274             :         {
    1275           0 :             report_invalid_record(state,
    1276             :                                   "WAL file is from different database system: WAL file database system identifier is %llu, pg_control database system identifier is %llu",
    1277           0 :                                   (unsigned long long) longhdr->xlp_sysid,
    1278           0 :                                   (unsigned long long) state->system_identifier);
    1279           0 :             return false;
    1280             :         }
    1281         112 :         else if (longhdr->xlp_seg_size != state->segcxt.ws_segsize)
    1282             :         {
    1283           0 :             report_invalid_record(state,
    1284             :                                   "WAL file is from different database system: incorrect segment size in page header");
    1285           0 :             return false;
    1286             :         }
    1287         112 :         else if (longhdr->xlp_xlog_blcksz != XLOG_BLCKSZ)
    1288             :         {
    1289           0 :             report_invalid_record(state,
    1290             :                                   "WAL file is from different database system: incorrect XLOG_BLCKSZ in page header");
    1291           0 :             return false;
    1292             :         }
    1293             :     }
    1294       11406 :     else if (offset == 0)
    1295             :     {
    1296             :         char        fname[MAXFNAMELEN];
    1297             : 
    1298           0 :         XLogFileName(fname, state->seg.ws_tli, segno, state->segcxt.ws_segsize);
    1299             : 
    1300             :         /* hmm, first page of file doesn't have a long header? */
    1301           0 :         report_invalid_record(state,
    1302             :                               "invalid info bits %04X in WAL segment %s, LSN %X/%X, offset %u",
    1303           0 :                               hdr->xlp_info,
    1304             :                               fname,
    1305           0 :                               LSN_FORMAT_ARGS(recptr),
    1306             :                               offset);
    1307           0 :         return false;
    1308             :     }
    1309             : 
    1310             :     /*
    1311             :      * Check that the address on the page agrees with what we expected. This
    1312             :      * check typically fails when an old WAL segment is recycled, and hasn't
    1313             :      * yet been overwritten with new data yet.
    1314             :      */
    1315       11518 :     if (hdr->xlp_pageaddr != recptr)
    1316             :     {
    1317             :         char        fname[MAXFNAMELEN];
    1318             : 
    1319           0 :         XLogFileName(fname, state->seg.ws_tli, segno, state->segcxt.ws_segsize);
    1320             : 
    1321           0 :         report_invalid_record(state,
    1322             :                               "unexpected pageaddr %X/%X in WAL segment %s, LSN %X/%X, offset %u",
    1323           0 :                               LSN_FORMAT_ARGS(hdr->xlp_pageaddr),
    1324             :                               fname,
    1325           0 :                               LSN_FORMAT_ARGS(recptr),
    1326             :                               offset);
    1327           0 :         return false;
    1328             :     }
    1329             : 
    1330             :     /*
    1331             :      * Since child timelines are always assigned a TLI greater than their
    1332             :      * immediate parent's TLI, we should never see TLI go backwards across
    1333             :      * successive pages of a consistent WAL sequence.
    1334             :      *
    1335             :      * Sometimes we re-read a segment that's already been (partially) read. So
    1336             :      * we only verify TLIs for pages that are later than the last remembered
    1337             :      * LSN.
    1338             :      */
    1339       11518 :     if (recptr > state->latestPagePtr)
    1340             :     {
    1341        8928 :         if (hdr->xlp_tli < state->latestPageTLI)
    1342             :         {
    1343             :             char        fname[MAXFNAMELEN];
    1344             : 
    1345           0 :             XLogFileName(fname, state->seg.ws_tli, segno, state->segcxt.ws_segsize);
    1346             : 
    1347           0 :             report_invalid_record(state,
    1348             :                                   "out-of-sequence timeline ID %u (after %u) in WAL segment %s, LSN %X/%X, offset %u",
    1349             :                                   hdr->xlp_tli,
    1350             :                                   state->latestPageTLI,
    1351             :                                   fname,
    1352           0 :                                   LSN_FORMAT_ARGS(recptr),
    1353             :                                   offset);
    1354           0 :             return false;
    1355             :         }
    1356             :     }
    1357       11518 :     state->latestPagePtr = recptr;
    1358       11518 :     state->latestPageTLI = hdr->xlp_tli;
    1359             : 
    1360       11518 :     return true;
    1361             : }
    1362             : 
    1363             : /*
    1364             :  * Forget about an error produced by XLogReaderValidatePageHeader().
    1365             :  */
    1366             : void
    1367           0 : XLogReaderResetError(XLogReaderState *state)
    1368             : {
    1369           0 :     state->errormsg_buf[0] = '\0';
    1370           0 :     state->errormsg_deferred = false;
    1371           0 : }
    1372             : 
    1373             : /*
    1374             :  * Find the first record with an lsn >= RecPtr.
    1375             :  *
    1376             :  * This is different from XLogBeginRead() in that RecPtr doesn't need to point
    1377             :  * to a valid record boundary.  Useful for checking whether RecPtr is a valid
    1378             :  * xlog address for reading, and to find the first valid address after some
    1379             :  * address when dumping records for debugging purposes.
    1380             :  *
    1381             :  * This positions the reader, like XLogBeginRead(), so that the next call to
    1382             :  * XLogReadRecord() will read the next valid record.
    1383             :  */
    1384             : XLogRecPtr
    1385           0 : XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
    1386             : {
    1387             :     XLogRecPtr  tmpRecPtr;
    1388           0 :     XLogRecPtr  found = InvalidXLogRecPtr;
    1389             :     XLogPageHeader header;
    1390             :     char       *errormsg;
    1391             : 
    1392             :     Assert(!XLogRecPtrIsInvalid(RecPtr));
    1393             : 
    1394             :     /* Make sure ReadPageInternal() can't return XLREAD_WOULDBLOCK. */
    1395           0 :     state->nonblocking = false;
    1396             : 
    1397             :     /*
    1398             :      * skip over potential continuation data, keeping in mind that it may span
    1399             :      * multiple pages
    1400             :      */
    1401           0 :     tmpRecPtr = RecPtr;
    1402             :     while (true)
    1403           0 :     {
    1404             :         XLogRecPtr  targetPagePtr;
    1405             :         int         targetRecOff;
    1406             :         uint32      pageHeaderSize;
    1407             :         int         readLen;
    1408             : 
    1409             :         /*
    1410             :          * Compute targetRecOff. It should typically be equal or greater than
    1411             :          * short page-header since a valid record can't start anywhere before
    1412             :          * that, except when caller has explicitly specified the offset that
    1413             :          * falls somewhere there or when we are skipping multi-page
    1414             :          * continuation record. It doesn't matter though because
    1415             :          * ReadPageInternal() is prepared to handle that and will read at
    1416             :          * least short page-header worth of data
    1417             :          */
    1418           0 :         targetRecOff = tmpRecPtr % XLOG_BLCKSZ;
    1419             : 
    1420             :         /* scroll back to page boundary */
    1421           0 :         targetPagePtr = tmpRecPtr - targetRecOff;
    1422             : 
    1423             :         /* Read the page containing the record */
    1424           0 :         readLen = ReadPageInternal(state, targetPagePtr, targetRecOff);
    1425           0 :         if (readLen < 0)
    1426           0 :             goto err;
    1427             : 
    1428           0 :         header = (XLogPageHeader) state->readBuf;
    1429             : 
    1430           0 :         pageHeaderSize = XLogPageHeaderSize(header);
    1431             : 
    1432             :         /* make sure we have enough data for the page header */
    1433           0 :         readLen = ReadPageInternal(state, targetPagePtr, pageHeaderSize);
    1434           0 :         if (readLen < 0)
    1435           0 :             goto err;
    1436             : 
    1437             :         /* skip over potential continuation data */
    1438           0 :         if (header->xlp_info & XLP_FIRST_IS_CONTRECORD)
    1439             :         {
    1440             :             /*
    1441             :              * If the length of the remaining continuation data is more than
    1442             :              * what can fit in this page, the continuation record crosses over
    1443             :              * this page. Read the next page and try again. xlp_rem_len in the
    1444             :              * next page header will contain the remaining length of the
    1445             :              * continuation data
    1446             :              *
    1447             :              * Note that record headers are MAXALIGN'ed
    1448             :              */
    1449           0 :             if (MAXALIGN(header->xlp_rem_len) >= (XLOG_BLCKSZ - pageHeaderSize))
    1450           0 :                 tmpRecPtr = targetPagePtr + XLOG_BLCKSZ;
    1451             :             else
    1452             :             {
    1453             :                 /*
    1454             :                  * The previous continuation record ends in this page. Set
    1455             :                  * tmpRecPtr to point to the first valid record
    1456             :                  */
    1457           0 :                 tmpRecPtr = targetPagePtr + pageHeaderSize
    1458           0 :                     + MAXALIGN(header->xlp_rem_len);
    1459           0 :                 break;
    1460             :             }
    1461             :         }
    1462             :         else
    1463             :         {
    1464           0 :             tmpRecPtr = targetPagePtr + pageHeaderSize;
    1465           0 :             break;
    1466             :         }
    1467             :     }
    1468             : 
    1469             :     /*
    1470             :      * we know now that tmpRecPtr is an address pointing to a valid XLogRecord
    1471             :      * because either we're at the first record after the beginning of a page
    1472             :      * or we just jumped over the remaining data of a continuation.
    1473             :      */
    1474           0 :     XLogBeginRead(state, tmpRecPtr);
    1475           0 :     while (XLogReadRecord(state, &errormsg) != NULL)
    1476             :     {
    1477             :         /* past the record we've found, break out */
    1478           0 :         if (RecPtr <= state->ReadRecPtr)
    1479             :         {
    1480             :             /* Rewind the reader to the beginning of the last record. */
    1481           0 :             found = state->ReadRecPtr;
    1482           0 :             XLogBeginRead(state, found);
    1483           0 :             return found;
    1484             :         }
    1485             :     }
    1486             : 
    1487           0 : err:
    1488           0 :     XLogReaderInvalReadState(state);
    1489             : 
    1490           0 :     return InvalidXLogRecPtr;
    1491             : }
    1492             : 
    1493             : /*
    1494             :  * Helper function to ease writing of XLogReaderRoutine->page_read callbacks.
    1495             :  * If this function is used, caller must supply a segment_open callback in
    1496             :  * 'state', as that is used here.
    1497             :  *
    1498             :  * Read 'count' bytes into 'buf', starting at location 'startptr', from WAL
    1499             :  * fetched from timeline 'tli'.
    1500             :  *
    1501             :  * Returns true if succeeded, false if an error occurs, in which case
    1502             :  * 'errinfo' receives error details.
    1503             :  *
    1504             :  * XXX probably this should be improved to suck data directly from the
    1505             :  * WAL buffers when possible.
    1506             :  */
    1507             : bool
    1508           0 : WALRead(XLogReaderState *state,
    1509             :         char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
    1510             :         WALReadError *errinfo)
    1511             : {
    1512             :     char       *p;
    1513             :     XLogRecPtr  recptr;
    1514             :     Size        nbytes;
    1515             : 
    1516           0 :     p = buf;
    1517           0 :     recptr = startptr;
    1518           0 :     nbytes = count;
    1519             : 
    1520           0 :     while (nbytes > 0)
    1521             :     {
    1522             :         uint32      startoff;
    1523             :         int         segbytes;
    1524             :         int         readbytes;
    1525             : 
    1526           0 :         startoff = XLogSegmentOffset(recptr, state->segcxt.ws_segsize);
    1527             : 
    1528             :         /*
    1529             :          * If the data we want is not in a segment we have open, close what we
    1530             :          * have (if anything) and open the next one, using the caller's
    1531             :          * provided segment_open callback.
    1532             :          */
    1533           0 :         if (state->seg.ws_file < 0 ||
    1534           0 :             !XLByteInSeg(recptr, state->seg.ws_segno, state->segcxt.ws_segsize) ||
    1535           0 :             tli != state->seg.ws_tli)
    1536             :         {
    1537             :             XLogSegNo   nextSegNo;
    1538             : 
    1539           0 :             if (state->seg.ws_file >= 0)
    1540           0 :                 state->routine.segment_close(state);
    1541             : 
    1542           0 :             XLByteToSeg(recptr, nextSegNo, state->segcxt.ws_segsize);
    1543           0 :             state->routine.segment_open(state, nextSegNo, &tli);
    1544             : 
    1545             :             /* This shouldn't happen -- indicates a bug in segment_open */
    1546             :             Assert(state->seg.ws_file >= 0);
    1547             : 
    1548             :             /* Update the current segment info. */
    1549           0 :             state->seg.ws_tli = tli;
    1550           0 :             state->seg.ws_segno = nextSegNo;
    1551             :         }
    1552             : 
    1553             :         /* How many bytes are within this segment? */
    1554           0 :         if (nbytes > (state->segcxt.ws_segsize - startoff))
    1555           0 :             segbytes = state->segcxt.ws_segsize - startoff;
    1556             :         else
    1557           0 :             segbytes = nbytes;
    1558             : 
    1559             : #ifndef FRONTEND
    1560             :         pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
    1561             : #endif
    1562             : 
    1563             :         /* Reset errno first; eases reporting non-errno-affecting errors */
    1564           0 :         errno = 0;
    1565           0 :         readbytes = pg_pread(state->seg.ws_file, p, segbytes, (off_t) startoff);
    1566             : 
    1567             : #ifndef FRONTEND
    1568             :         pgstat_report_wait_end();
    1569             : #endif
    1570             : 
    1571           0 :         if (readbytes <= 0)
    1572             :         {
    1573           0 :             errinfo->wre_errno = errno;
    1574           0 :             errinfo->wre_req = segbytes;
    1575           0 :             errinfo->wre_read = readbytes;
    1576           0 :             errinfo->wre_off = startoff;
    1577           0 :             errinfo->wre_seg = state->seg;
    1578           0 :             return false;
    1579             :         }
    1580             : 
    1581             :         /* Update state for read */
    1582           0 :         recptr += readbytes;
    1583           0 :         nbytes -= readbytes;
    1584           0 :         p += readbytes;
    1585             :     }
    1586             : 
    1587           0 :     return true;
    1588             : }
    1589             : 
    1590             : /* ----------------------------------------
    1591             :  * Functions for decoding the data and block references in a record.
    1592             :  * ----------------------------------------
    1593             :  */
    1594             : 
    1595             : /*
    1596             :  * Private function to reset the state, forgetting all decoded records, if we
    1597             :  * are asked to move to a new read position.
    1598             :  */
    1599             : static void
    1600        5200 : ResetDecoder(XLogReaderState *state)
    1601             : {
    1602             :     DecodedXLogRecord *r;
    1603             : 
    1604             :     /* Reset the decoded record queue, freeing any oversized records. */
    1605       10322 :     while ((r = state->decode_queue_head) != NULL)
    1606             :     {
    1607        5122 :         state->decode_queue_head = r->next;
    1608        5122 :         if (r->oversized)
    1609           0 :             pfree(r);
    1610             :     }
    1611        5200 :     state->decode_queue_tail = NULL;
    1612        5200 :     state->decode_queue_head = NULL;
    1613        5200 :     state->record = NULL;
    1614             : 
    1615             :     /* Reset the decode buffer to empty. */
    1616        5200 :     state->decode_buffer_tail = state->decode_buffer;
    1617        5200 :     state->decode_buffer_head = state->decode_buffer;
    1618             : 
    1619             :     /* Clear error state. */
    1620        5200 :     state->errormsg_buf[0] = '\0';
    1621        5200 :     state->errormsg_deferred = false;
    1622        5200 : }
    1623             : 
    1624             : /*
    1625             :  * Compute the maximum possible amount of padding that could be required to
    1626             :  * decode a record, given xl_tot_len from the record's header.  This is the
    1627             :  * amount of output buffer space that we need to decode a record, though we
    1628             :  * might not finish up using it all.
    1629             :  *
    1630             :  * This computation is pessimistic and assumes the maximum possible number of
    1631             :  * blocks, due to lack of better information.
    1632             :  */
    1633             : size_t
    1634      178544 : DecodeXLogRecordRequiredSpace(size_t xl_tot_len)
    1635             : {
    1636      178544 :     size_t      size = 0;
    1637             : 
    1638             :     /* Account for the fixed size part of the decoded record struct. */
    1639      178544 :     size += offsetof(DecodedXLogRecord, blocks[0]);
    1640             :     /* Account for the flexible blocks array of maximum possible size. */
    1641      178544 :     size += sizeof(DecodedBkpBlock) * (XLR_MAX_BLOCK_ID + 1);
    1642             :     /* Account for all the raw main and block data. */
    1643      178544 :     size += xl_tot_len;
    1644             :     /* We might insert padding before main_data. */
    1645      178544 :     size += (MAXIMUM_ALIGNOF - 1);
    1646             :     /* We might insert padding before each block's data. */
    1647      178544 :     size += (MAXIMUM_ALIGNOF - 1) * (XLR_MAX_BLOCK_ID + 1);
    1648             :     /* We might insert padding at the end. */
    1649      178544 :     size += (MAXIMUM_ALIGNOF - 1);
    1650             : 
    1651      178544 :     return size;
    1652             : }
    1653             : 
    1654             : /*
    1655             :  * Decode a record.  "decoded" must point to a MAXALIGNed memory area that has
    1656             :  * space for at least DecodeXLogRecordRequiredSpace(record) bytes.  On
    1657             :  * success, decoded->size contains the actual space occupied by the decoded
    1658             :  * record, which may turn out to be less.
    1659             :  *
    1660             :  * Only decoded->oversized member must be initialized already, and will not be
    1661             :  * modified.  Other members will be initialized as required.
    1662             :  *
    1663             :  * On error, a human-readable error message is returned in *errormsg, and
    1664             :  * the return value is false.
    1665             :  */
    1666             : bool
    1667      178544 : DecodeXLogRecord(XLogReaderState *state,
    1668             :                  DecodedXLogRecord *decoded,
    1669             :                  XLogRecord *record,
    1670             :                  XLogRecPtr lsn,
    1671             :                  char **errormsg)
    1672             : {
    1673             :     /*
    1674             :      * read next _size bytes from record buffer, but check for overrun first.
    1675             :      */
    1676             : #define COPY_HEADER_FIELD(_dst, _size)          \
    1677             :     do {                                        \
    1678             :         if (remaining < _size)                   \
    1679             :             goto shortdata_err;                 \
    1680             :         memcpy(_dst, ptr, _size);               \
    1681             :         ptr += _size;                           \
    1682             :         remaining -= _size;                     \
    1683             :     } while(0)
    1684             : 
    1685             :     char       *ptr;
    1686             :     char       *out;
    1687             :     uint32      remaining;
    1688             :     uint32      datatotal;
    1689      178544 :     RelFileLocator *rlocator = NULL;
    1690             :     uint8       block_id;
    1691             : 
    1692      178544 :     decoded->header = *record;
    1693      178544 :     decoded->lsn = lsn;
    1694      178544 :     decoded->next = NULL;
    1695      178544 :     decoded->record_origin = InvalidRepOriginId;
    1696      178544 :     decoded->toplevel_xid = InvalidTransactionId;
    1697      178544 :     decoded->main_data = NULL;
    1698      178544 :     decoded->main_data_len = 0;
    1699      178544 :     decoded->max_block_id = -1;
    1700      178544 :     ptr = (char *) record;
    1701      178544 :     ptr += SizeOfXLogRecord;
    1702      178544 :     remaining = record->xl_tot_len - SizeOfXLogRecord;
    1703             : 
    1704             :     /* Decode the headers */
    1705      178544 :     datatotal = 0;
    1706      353880 :     while (remaining > datatotal)
    1707             :     {
    1708      341958 :         COPY_HEADER_FIELD(&block_id, sizeof(uint8));
    1709             : 
    1710      341958 :         if (block_id == XLR_BLOCK_ID_DATA_SHORT)
    1711             :         {
    1712             :             /* XLogRecordDataHeaderShort */
    1713             :             uint8       main_data_len;
    1714             : 
    1715      166590 :             COPY_HEADER_FIELD(&main_data_len, sizeof(uint8));
    1716             : 
    1717      166590 :             decoded->main_data_len = main_data_len;
    1718      166590 :             datatotal += main_data_len;
    1719      166590 :             break;              /* by convention, the main data fragment is
    1720             :                                  * always last */
    1721             :         }
    1722      175368 :         else if (block_id == XLR_BLOCK_ID_DATA_LONG)
    1723             :         {
    1724             :             /* XLogRecordDataHeaderLong */
    1725             :             uint32      main_data_len;
    1726             : 
    1727          32 :             COPY_HEADER_FIELD(&main_data_len, sizeof(uint32));
    1728          32 :             decoded->main_data_len = main_data_len;
    1729          32 :             datatotal += main_data_len;
    1730          32 :             break;              /* by convention, the main data fragment is
    1731             :                                  * always last */
    1732             :         }
    1733      175336 :         else if (block_id == XLR_BLOCK_ID_ORIGIN)
    1734             :         {
    1735           0 :             COPY_HEADER_FIELD(&decoded->record_origin, sizeof(RepOriginId));
    1736             :         }
    1737      175336 :         else if (block_id == XLR_BLOCK_ID_TOPLEVEL_XID)
    1738             :         {
    1739           0 :             COPY_HEADER_FIELD(&decoded->toplevel_xid, sizeof(TransactionId));
    1740             :         }
    1741      175336 :         else if (block_id <= XLR_MAX_BLOCK_ID)
    1742             :         {
    1743             :             /* XLogRecordBlockHeader */
    1744             :             DecodedBkpBlock *blk;
    1745             :             uint8       fork_flags;
    1746             : 
    1747             :             /* mark any intervening block IDs as not in use */
    1748      175336 :             for (int i = decoded->max_block_id + 1; i < block_id; ++i)
    1749           0 :                 decoded->blocks[i].in_use = false;
    1750             : 
    1751      175336 :             if (block_id <= decoded->max_block_id)
    1752             :             {
    1753           0 :                 report_invalid_record(state,
    1754             :                                       "out-of-order block_id %u at %X/%X",
    1755             :                                       block_id,
    1756           0 :                                       LSN_FORMAT_ARGS(state->ReadRecPtr));
    1757           0 :                 goto err;
    1758             :             }
    1759      175336 :             decoded->max_block_id = block_id;
    1760             : 
    1761      175336 :             blk = &decoded->blocks[block_id];
    1762      175336 :             blk->in_use = true;
    1763      175336 :             blk->apply_image = false;
    1764             : 
    1765      175336 :             COPY_HEADER_FIELD(&fork_flags, sizeof(uint8));
    1766      175336 :             blk->forknum = fork_flags & BKPBLOCK_FORK_MASK;
    1767      175336 :             blk->flags = fork_flags;
    1768      175336 :             blk->has_image = ((fork_flags & BKPBLOCK_HAS_IMAGE) != 0);
    1769      175336 :             blk->has_data = ((fork_flags & BKPBLOCK_HAS_DATA) != 0);
    1770             : 
    1771      175336 :             blk->prefetch_buffer = InvalidBuffer;
    1772             : 
    1773      175336 :             COPY_HEADER_FIELD(&blk->data_len, sizeof(uint16));
    1774             :             /* cross-check that the HAS_DATA flag is set iff data_length > 0 */
    1775      175336 :             if (blk->has_data && blk->data_len == 0)
    1776             :             {
    1777           0 :                 report_invalid_record(state,
    1778             :                                       "BKPBLOCK_HAS_DATA set, but no data included at %X/%X",
    1779           0 :                                       LSN_FORMAT_ARGS(state->ReadRecPtr));
    1780           0 :                 goto err;
    1781             :             }
    1782      175336 :             if (!blk->has_data && blk->data_len != 0)
    1783             :             {
    1784           0 :                 report_invalid_record(state,
    1785             :                                       "BKPBLOCK_HAS_DATA not set, but data length is %u at %X/%X",
    1786           0 :                                       (unsigned int) blk->data_len,
    1787           0 :                                       LSN_FORMAT_ARGS(state->ReadRecPtr));
    1788           0 :                 goto err;
    1789             :             }
    1790      175336 :             datatotal += blk->data_len;
    1791             : 
    1792      175336 :             if (blk->has_image)
    1793             :             {
    1794       11998 :                 COPY_HEADER_FIELD(&blk->bimg_len, sizeof(uint16));
    1795       11998 :                 COPY_HEADER_FIELD(&blk->hole_offset, sizeof(uint16));
    1796       11998 :                 COPY_HEADER_FIELD(&blk->bimg_info, sizeof(uint8));
    1797             : 
    1798       11998 :                 blk->apply_image = ((blk->bimg_info & BKPIMAGE_APPLY) != 0);
    1799             : 
    1800       11998 :                 if (BKPIMAGE_COMPRESSED(blk->bimg_info))
    1801             :                 {
    1802           0 :                     if (blk->bimg_info & BKPIMAGE_HAS_HOLE)
    1803           0 :                         COPY_HEADER_FIELD(&blk->hole_length, sizeof(uint16));
    1804             :                     else
    1805           0 :                         blk->hole_length = 0;
    1806             :                 }
    1807             :                 else
    1808       11998 :                     blk->hole_length = BLCKSZ - blk->bimg_len;
    1809       11998 :                 datatotal += blk->bimg_len;
    1810             : 
    1811             :                 /*
    1812             :                  * cross-check that hole_offset > 0, hole_length > 0 and
    1813             :                  * bimg_len < BLCKSZ if the HAS_HOLE flag is set.
    1814             :                  */
    1815       11998 :                 if ((blk->bimg_info & BKPIMAGE_HAS_HOLE) &&
    1816       11902 :                     (blk->hole_offset == 0 ||
    1817       11902 :                      blk->hole_length == 0 ||
    1818       11902 :                      blk->bimg_len == BLCKSZ))
    1819             :                 {
    1820           0 :                     report_invalid_record(state,
    1821             :                                           "BKPIMAGE_HAS_HOLE set, but hole offset %u length %u block image length %u at %X/%X",
    1822           0 :                                           (unsigned int) blk->hole_offset,
    1823           0 :                                           (unsigned int) blk->hole_length,
    1824           0 :                                           (unsigned int) blk->bimg_len,
    1825           0 :                                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1826           0 :                     goto err;
    1827             :                 }
    1828             : 
    1829             :                 /*
    1830             :                  * cross-check that hole_offset == 0 and hole_length == 0 if
    1831             :                  * the HAS_HOLE flag is not set.
    1832             :                  */
    1833       11998 :                 if (!(blk->bimg_info & BKPIMAGE_HAS_HOLE) &&
    1834          96 :                     (blk->hole_offset != 0 || blk->hole_length != 0))
    1835             :                 {
    1836           0 :                     report_invalid_record(state,
    1837             :                                           "BKPIMAGE_HAS_HOLE not set, but hole offset %u length %u at %X/%X",
    1838           0 :                                           (unsigned int) blk->hole_offset,
    1839           0 :                                           (unsigned int) blk->hole_length,
    1840           0 :                                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1841           0 :                     goto err;
    1842             :                 }
    1843             : 
    1844             :                 /*
    1845             :                  * Cross-check that bimg_len < BLCKSZ if it is compressed.
    1846             :                  */
    1847       11998 :                 if (BKPIMAGE_COMPRESSED(blk->bimg_info) &&
    1848           0 :                     blk->bimg_len == BLCKSZ)
    1849             :                 {
    1850           0 :                     report_invalid_record(state,
    1851             :                                           "BKPIMAGE_COMPRESSED set, but block image length %u at %X/%X",
    1852           0 :                                           (unsigned int) blk->bimg_len,
    1853           0 :                                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1854           0 :                     goto err;
    1855             :                 }
    1856             : 
    1857             :                 /*
    1858             :                  * cross-check that bimg_len = BLCKSZ if neither HAS_HOLE is
    1859             :                  * set nor COMPRESSED().
    1860             :                  */
    1861       11998 :                 if (!(blk->bimg_info & BKPIMAGE_HAS_HOLE) &&
    1862          96 :                     !BKPIMAGE_COMPRESSED(blk->bimg_info) &&
    1863          96 :                     blk->bimg_len != BLCKSZ)
    1864             :                 {
    1865           0 :                     report_invalid_record(state,
    1866             :                                           "neither BKPIMAGE_HAS_HOLE nor BKPIMAGE_COMPRESSED set, but block image length is %u at %X/%X",
    1867           0 :                                           (unsigned int) blk->data_len,
    1868           0 :                                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1869           0 :                     goto err;
    1870             :                 }
    1871             :             }
    1872      175336 :             if (!(fork_flags & BKPBLOCK_SAME_REL))
    1873             :             {
    1874      174640 :                 COPY_HEADER_FIELD(&blk->rlocator, sizeof(RelFileLocator));
    1875      174640 :                 rlocator = &blk->rlocator;
    1876             :             }
    1877             :             else
    1878             :             {
    1879         696 :                 if (rlocator == NULL)
    1880             :                 {
    1881           0 :                     report_invalid_record(state,
    1882             :                                           "BKPBLOCK_SAME_REL set but no previous rel at %X/%X",
    1883           0 :                                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1884           0 :                     goto err;
    1885             :                 }
    1886             : 
    1887         696 :                 blk->rlocator = *rlocator;
    1888             :             }
    1889      175336 :             COPY_HEADER_FIELD(&blk->blkno, sizeof(BlockNumber));
    1890             :         }
    1891             :         else
    1892             :         {
    1893           0 :             report_invalid_record(state,
    1894             :                                   "invalid block_id %u at %X/%X",
    1895           0 :                                   block_id, LSN_FORMAT_ARGS(state->ReadRecPtr));
    1896           0 :             goto err;
    1897             :         }
    1898             :     }
    1899             : 
    1900      178544 :     if (remaining != datatotal)
    1901           0 :         goto shortdata_err;
    1902             : 
    1903             :     /*
    1904             :      * Ok, we've parsed the fragment headers, and verified that the total
    1905             :      * length of the payload in the fragments is equal to the amount of data
    1906             :      * left.  Copy the data of each fragment to contiguous space after the
    1907             :      * blocks array, inserting alignment padding before the data fragments so
    1908             :      * they can be cast to struct pointers by REDO routines.
    1909             :      */
    1910      178544 :     out = ((char *) decoded) +
    1911      178544 :         offsetof(DecodedXLogRecord, blocks) +
    1912      178544 :         sizeof(decoded->blocks[0]) * (decoded->max_block_id + 1);
    1913             : 
    1914             :     /* block data first */
    1915      353880 :     for (block_id = 0; block_id <= decoded->max_block_id; block_id++)
    1916             :     {
    1917      175336 :         DecodedBkpBlock *blk = &decoded->blocks[block_id];
    1918             : 
    1919      175336 :         if (!blk->in_use)
    1920           0 :             continue;
    1921             : 
    1922             :         Assert(blk->has_image || !blk->apply_image);
    1923             : 
    1924      175336 :         if (blk->has_image)
    1925             :         {
    1926             :             /* no need to align image */
    1927       11998 :             blk->bkp_image = out;
    1928       11998 :             memcpy(out, ptr, blk->bimg_len);
    1929       11998 :             ptr += blk->bimg_len;
    1930       11998 :             out += blk->bimg_len;
    1931             :         }
    1932      175336 :         if (blk->has_data)
    1933             :         {
    1934       81826 :             out = (char *) MAXALIGN(out);
    1935       81826 :             blk->data = out;
    1936       81826 :             memcpy(blk->data, ptr, blk->data_len);
    1937       81826 :             ptr += blk->data_len;
    1938       81826 :             out += blk->data_len;
    1939             :         }
    1940             :     }
    1941             : 
    1942             :     /* and finally, the main data */
    1943      178544 :     if (decoded->main_data_len > 0)
    1944             :     {
    1945      166622 :         out = (char *) MAXALIGN(out);
    1946      166622 :         decoded->main_data = out;
    1947      166622 :         memcpy(decoded->main_data, ptr, decoded->main_data_len);
    1948      166622 :         ptr += decoded->main_data_len;
    1949      166622 :         out += decoded->main_data_len;
    1950             :     }
    1951             : 
    1952             :     /* Report the actual size we used. */
    1953      178544 :     decoded->size = MAXALIGN(out - (char *) decoded);
    1954             :     Assert(DecodeXLogRecordRequiredSpace(record->xl_tot_len) >=
    1955             :            decoded->size);
    1956             : 
    1957      178544 :     return true;
    1958             : 
    1959           0 : shortdata_err:
    1960           0 :     report_invalid_record(state,
    1961             :                           "record with invalid length at %X/%X",
    1962           0 :                           LSN_FORMAT_ARGS(state->ReadRecPtr));
    1963           0 : err:
    1964           0 :     *errormsg = state->errormsg_buf;
    1965             : 
    1966           0 :     return false;
    1967             : }
    1968             : 
    1969             : /*
    1970             :  * Returns information about the block that a block reference refers to.
    1971             :  *
    1972             :  * This is like XLogRecGetBlockTagExtended, except that the block reference
    1973             :  * must exist and there's no access to prefetch_buffer.
    1974             :  */
    1975             : void
    1976           0 : XLogRecGetBlockTag(XLogReaderState *record, uint8 block_id,
    1977             :                    RelFileLocator *rlocator, ForkNumber *forknum,
    1978             :                    BlockNumber *blknum)
    1979             : {
    1980           0 :     if (!XLogRecGetBlockTagExtended(record, block_id, rlocator, forknum,
    1981             :                                     blknum, NULL))
    1982             :     {
    1983             : #ifndef FRONTEND
    1984             :         elog(ERROR, "could not locate backup block with ID %d in WAL record",
    1985             :              block_id);
    1986             : #else
    1987           0 :         pg_fatal("could not locate backup block with ID %d in WAL record",
    1988             :                  block_id);
    1989             : #endif
    1990             :     }
    1991           0 : }
    1992             : 
    1993             : /*
    1994             :  * Returns information about the block that a block reference refers to,
    1995             :  * optionally including the buffer that the block may already be in.
    1996             :  *
    1997             :  * If the WAL record contains a block reference with the given ID, *rlocator,
    1998             :  * *forknum, *blknum and *prefetch_buffer are filled in (if not NULL), and
    1999             :  * returns true.  Otherwise returns false.
    2000             :  */
    2001             : bool
    2002      171432 : XLogRecGetBlockTagExtended(XLogReaderState *record, uint8 block_id,
    2003             :                            RelFileLocator *rlocator, ForkNumber *forknum,
    2004             :                            BlockNumber *blknum,
    2005             :                            Buffer *prefetch_buffer)
    2006             : {
    2007             :     DecodedBkpBlock *bkpb;
    2008             : 
    2009      171432 :     if (!XLogRecHasBlockRef(record, block_id))
    2010           0 :         return false;
    2011             : 
    2012      171432 :     bkpb = &record->record->blocks[block_id];
    2013      171432 :     if (rlocator)
    2014      171432 :         *rlocator = bkpb->rlocator;
    2015      171432 :     if (forknum)
    2016      171432 :         *forknum = bkpb->forknum;
    2017      171432 :     if (blknum)
    2018      171432 :         *blknum = bkpb->blkno;
    2019      171432 :     if (prefetch_buffer)
    2020           0 :         *prefetch_buffer = bkpb->prefetch_buffer;
    2021      171432 :     return true;
    2022             : }
    2023             : 
    2024             : /*
    2025             :  * Returns the data associated with a block reference, or NULL if there is
    2026             :  * no data (e.g. because a full-page image was taken instead). The returned
    2027             :  * pointer points to a MAXALIGNed buffer.
    2028             :  */
    2029             : char *
    2030           0 : XLogRecGetBlockData(XLogReaderState *record, uint8 block_id, Size *len)
    2031             : {
    2032             :     DecodedBkpBlock *bkpb;
    2033             : 
    2034           0 :     if (block_id > record->record->max_block_id ||
    2035           0 :         !record->record->blocks[block_id].in_use)
    2036           0 :         return NULL;
    2037             : 
    2038           0 :     bkpb = &record->record->blocks[block_id];
    2039             : 
    2040           0 :     if (!bkpb->has_data)
    2041             :     {
    2042           0 :         if (len)
    2043           0 :             *len = 0;
    2044           0 :         return NULL;
    2045             :     }
    2046             :     else
    2047             :     {
    2048           0 :         if (len)
    2049           0 :             *len = bkpb->data_len;
    2050           0 :         return bkpb->data;
    2051             :     }
    2052             : }
    2053             : 
    2054             : /*
    2055             :  * Restore a full-page image from a backup block attached to an XLOG record.
    2056             :  *
    2057             :  * Returns true if a full-page image is restored, and false on failure with
    2058             :  * an error to be consumed by the caller.
    2059             :  */
    2060             : bool
    2061           0 : RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
    2062             : {
    2063             :     DecodedBkpBlock *bkpb;
    2064             :     char       *ptr;
    2065             :     PGAlignedBlock tmp;
    2066             : 
    2067           0 :     if (block_id > record->record->max_block_id ||
    2068           0 :         !record->record->blocks[block_id].in_use)
    2069             :     {
    2070           0 :         report_invalid_record(record,
    2071             :                               "could not restore image at %X/%X with invalid block %d specified",
    2072           0 :                               LSN_FORMAT_ARGS(record->ReadRecPtr),
    2073             :                               block_id);
    2074           0 :         return false;
    2075             :     }
    2076           0 :     if (!record->record->blocks[block_id].has_image)
    2077             :     {
    2078           0 :         report_invalid_record(record, "could not restore image at %X/%X with invalid state, block %d",
    2079           0 :                               LSN_FORMAT_ARGS(record->ReadRecPtr),
    2080             :                               block_id);
    2081           0 :         return false;
    2082             :     }
    2083             : 
    2084           0 :     bkpb = &record->record->blocks[block_id];
    2085           0 :     ptr = bkpb->bkp_image;
    2086             : 
    2087           0 :     if (BKPIMAGE_COMPRESSED(bkpb->bimg_info))
    2088             :     {
    2089             :         /* If a backup block image is compressed, decompress it */
    2090           0 :         bool        decomp_success = true;
    2091             : 
    2092           0 :         if ((bkpb->bimg_info & BKPIMAGE_COMPRESS_PGLZ) != 0)
    2093             :         {
    2094           0 :             if (pglz_decompress(ptr, bkpb->bimg_len, tmp.data,
    2095           0 :                                 BLCKSZ - bkpb->hole_length, true) < 0)
    2096           0 :                 decomp_success = false;
    2097             :         }
    2098           0 :         else if ((bkpb->bimg_info & BKPIMAGE_COMPRESS_LZ4) != 0)
    2099             :         {
    2100             : #ifdef USE_LZ4
    2101           0 :             if (LZ4_decompress_safe(ptr, tmp.data,
    2102           0 :                                     bkpb->bimg_len, BLCKSZ - bkpb->hole_length) <= 0)
    2103           0 :                 decomp_success = false;
    2104             : #else
    2105             :             report_invalid_record(record, "could not restore image at %X/%X compressed with %s not supported by build, block %d",
    2106             :                                   LSN_FORMAT_ARGS(record->ReadRecPtr),
    2107             :                                   "LZ4",
    2108             :                                   block_id);
    2109             :             return false;
    2110             : #endif
    2111             :         }
    2112           0 :         else if ((bkpb->bimg_info & BKPIMAGE_COMPRESS_ZSTD) != 0)
    2113             :         {
    2114             : #ifdef USE_ZSTD
    2115             :             size_t      decomp_result = ZSTD_decompress(tmp.data,
    2116             :                                                         BLCKSZ - bkpb->hole_length,
    2117             :                                                         ptr, bkpb->bimg_len);
    2118             : 
    2119             :             if (ZSTD_isError(decomp_result))
    2120             :                 decomp_success = false;
    2121             : #else
    2122           0 :             report_invalid_record(record, "could not restore image at %X/%X compressed with %s not supported by build, block %d",
    2123           0 :                                   LSN_FORMAT_ARGS(record->ReadRecPtr),
    2124             :                                   "zstd",
    2125             :                                   block_id);
    2126           0 :             return false;
    2127             : #endif
    2128             :         }
    2129             :         else
    2130             :         {
    2131           0 :             report_invalid_record(record, "could not restore image at %X/%X compressed with unknown method, block %d",
    2132           0 :                                   LSN_FORMAT_ARGS(record->ReadRecPtr),
    2133             :                                   block_id);
    2134           0 :             return false;
    2135             :         }
    2136             : 
    2137           0 :         if (!decomp_success)
    2138             :         {
    2139           0 :             report_invalid_record(record, "could not decompress image at %X/%X, block %d",
    2140           0 :                                   LSN_FORMAT_ARGS(record->ReadRecPtr),
    2141             :                                   block_id);
    2142           0 :             return false;
    2143             :         }
    2144             : 
    2145           0 :         ptr = tmp.data;
    2146             :     }
    2147             : 
    2148             :     /* generate page, taking into account hole if necessary */
    2149           0 :     if (bkpb->hole_length == 0)
    2150             :     {
    2151           0 :         memcpy(page, ptr, BLCKSZ);
    2152             :     }
    2153             :     else
    2154             :     {
    2155           0 :         memcpy(page, ptr, bkpb->hole_offset);
    2156             :         /* must zero-fill the hole */
    2157           0 :         MemSet(page + bkpb->hole_offset, 0, bkpb->hole_length);
    2158           0 :         memcpy(page + (bkpb->hole_offset + bkpb->hole_length),
    2159           0 :                ptr + bkpb->hole_offset,
    2160           0 :                BLCKSZ - (bkpb->hole_offset + bkpb->hole_length));
    2161             :     }
    2162             : 
    2163           0 :     return true;
    2164             : }
    2165             : 
    2166             : #ifndef FRONTEND
    2167             : 
    2168             : /*
    2169             :  * Extract the FullTransactionId from a WAL record.
    2170             :  */
    2171             : FullTransactionId
    2172             : XLogRecGetFullXid(XLogReaderState *record)
    2173             : {
    2174             :     TransactionId xid,
    2175             :                 next_xid;
    2176             :     uint32      epoch;
    2177             : 
    2178             :     /*
    2179             :      * This function is only safe during replay, because it depends on the
    2180             :      * replay state.  See AdvanceNextFullTransactionIdPastXid() for more.
    2181             :      */
    2182             :     Assert(AmStartupProcess() || !IsUnderPostmaster);
    2183             : 
    2184             :     xid = XLogRecGetXid(record);
    2185             :     next_xid = XidFromFullTransactionId(TransamVariables->nextXid);
    2186             :     epoch = EpochFromFullTransactionId(TransamVariables->nextXid);
    2187             : 
    2188             :     /*
    2189             :      * If xid is numerically greater than next_xid, it has to be from the last
    2190             :      * epoch.
    2191             :      */
    2192             :     if (unlikely(xid > next_xid))
    2193             :         --epoch;
    2194             : 
    2195             :     return FullTransactionIdFromEpochAndXid(epoch, xid);
    2196             : }
    2197             : 
    2198             : #endif

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