Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * buf_table.c
       4             :  *    routines for mapping BufferTags to buffer indexes.
       5             :  *
       6             :  * Note: the routines in this file do no locking of their own.  The caller
       7             :  * must hold a suitable lock on the appropriate BufMappingLock, as specified
       8             :  * in the comments.  We can't do the locking inside these functions because
       9             :  * in most cases the caller needs to adjust the buffer header contents
      10             :  * before the lock is released (see notes in README).
      11             :  *
      12             :  *
      13             :  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
      14             :  * Portions Copyright (c) 1994, Regents of the University of California
      15             :  *
      16             :  *
      17             :  * IDENTIFICATION
      18             :  *    src/backend/storage/buffer/buf_table.c
      19             :  *
      20             :  *-------------------------------------------------------------------------
      21             :  */
      22             : #include "postgres.h"
      23             : 
      24             : #include "storage/buf_internals.h"
      25             : #include "storage/bufmgr.h"
      26             : 
      27             : /* entry for buffer lookup hashtable */
      28             : typedef struct
      29             : {
      30             :     BufferTag   key;            /* Tag of a disk page */
      31             :     int         id;             /* Associated buffer ID */
      32             : } BufferLookupEnt;
      33             : 
      34             : static HTAB *SharedBufHash;
      35             : 
      36             : 
      37             : /*
      38             :  * Estimate space needed for mapping hashtable
      39             :  *      size is the desired hash table size (possibly more than NBuffers)
      40             :  */
      41             : Size
      42        5456 : BufTableShmemSize(int size)
      43             : {
      44        5456 :     return hash_estimate_size(size, sizeof(BufferLookupEnt));
      45             : }
      46             : 
      47             : /*
      48             :  * Initialize shmem hash table for mapping buffers
      49             :  *      size is the desired hash table size (possibly more than NBuffers)
      50             :  */
      51             : void
      52        3636 : InitBufTable(int size)
      53             : {
      54             :     HASHCTL     info;
      55             : 
      56             :     /* assume no locking is needed yet */
      57             : 
      58             :     /* BufferTag maps to Buffer */
      59        3636 :     info.keysize = sizeof(BufferTag);
      60        3636 :     info.entrysize = sizeof(BufferLookupEnt);
      61        3636 :     info.num_partitions = NUM_BUFFER_PARTITIONS;
      62             : 
      63        3636 :     SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
      64             :                                   size, size,
      65             :                                   &info,
      66             :                                   HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
      67        3636 : }
      68             : 
      69             : /*
      70             :  * BufTableHashCode
      71             :  *      Compute the hash code associated with a BufferTag
      72             :  *
      73             :  * This must be passed to the lookup/insert/delete routines along with the
      74             :  * tag.  We do it like this because the callers need to know the hash code
      75             :  * in order to determine which buffer partition to lock, and we don't want
      76             :  * to do the hash computation twice (hash_any is a bit slow).
      77             :  */
      78             : uint32
      79   137604542 : BufTableHashCode(BufferTag *tagPtr)
      80             : {
      81   137604542 :     return get_hash_value(SharedBufHash, (void *) tagPtr);
      82             : }
      83             : 
      84             : /*
      85             :  * BufTableLookup
      86             :  *      Lookup the given BufferTag; return buffer ID, or -1 if not found
      87             :  *
      88             :  * Caller must hold at least share lock on BufMappingLock for tag's partition
      89             :  */
      90             : int
      91   134675148 : BufTableLookup(BufferTag *tagPtr, uint32 hashcode)
      92             : {
      93             :     BufferLookupEnt *result;
      94             : 
      95             :     result = (BufferLookupEnt *)
      96   134675148 :         hash_search_with_hash_value(SharedBufHash,
      97             :                                     tagPtr,
      98             :                                     hashcode,
      99             :                                     HASH_FIND,
     100             :                                     NULL);
     101             : 
     102   134675148 :     if (!result)
     103     3333410 :         return -1;
     104             : 
     105   131341738 :     return result->id;
     106             : }
     107             : 
     108             : /*
     109             :  * BufTableInsert
     110             :  *      Insert a hashtable entry for given tag and buffer ID,
     111             :  *      unless an entry already exists for that tag
     112             :  *
     113             :  * Returns -1 on successful insertion.  If a conflicting entry exists
     114             :  * already, returns the buffer ID in that entry.
     115             :  *
     116             :  * Caller must hold exclusive lock on BufMappingLock for tag's partition
     117             :  */
     118             : int
     119     3641766 : BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id)
     120             : {
     121             :     BufferLookupEnt *result;
     122             :     bool        found;
     123             : 
     124             :     Assert(buf_id >= 0);     /* -1 is reserved for not-in-table */
     125             :     Assert(tagPtr->blockNum != P_NEW);   /* invalid tag */
     126             : 
     127             :     result = (BufferLookupEnt *)
     128     3641766 :         hash_search_with_hash_value(SharedBufHash,
     129             :                                     tagPtr,
     130             :                                     hashcode,
     131             :                                     HASH_ENTER,
     132             :                                     &found);
     133             : 
     134     3641766 :     if (found)                  /* found something already in the table */
     135         250 :         return result->id;
     136             : 
     137     3641516 :     result->id = buf_id;
     138             : 
     139     3641516 :     return -1;
     140             : }
     141             : 
     142             : /*
     143             :  * BufTableDelete
     144             :  *      Delete the hashtable entry for given tag (which must exist)
     145             :  *
     146             :  * Caller must hold exclusive lock on BufMappingLock for tag's partition
     147             :  */
     148             : void
     149     2204376 : BufTableDelete(BufferTag *tagPtr, uint32 hashcode)
     150             : {
     151             :     BufferLookupEnt *result;
     152             : 
     153             :     result = (BufferLookupEnt *)
     154     2204376 :         hash_search_with_hash_value(SharedBufHash,
     155             :                                     tagPtr,
     156             :                                     hashcode,
     157             :                                     HASH_REMOVE,
     158             :                                     NULL);
     159             : 
     160     2204376 :     if (!result)                /* shouldn't happen */
     161           0 :         elog(ERROR, "shared buffer hash table corrupted");
     162     2204376 : }