Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * buf_init.c
       4             :  *    buffer manager initialization routines
       5             :  *
       6             :  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
       7             :  * Portions Copyright (c) 1994, Regents of the University of California
       8             :  *
       9             :  *
      10             :  * IDENTIFICATION
      11             :  *    src/backend/storage/buffer/buf_init.c
      12             :  *
      13             :  *-------------------------------------------------------------------------
      14             :  */
      15             : #include "postgres.h"
      16             : 
      17             : #include "storage/buf_internals.h"
      18             : #include "storage/bufmgr.h"
      19             : 
      20             : BufferDescPadded *BufferDescriptors;
      21             : char       *BufferBlocks;
      22             : ConditionVariableMinimallyPadded *BufferIOCVArray;
      23             : WritebackContext BackendWritebackContext;
      24             : CkptSortItem *CkptBufferIds;
      25             : 
      26             : 
      27             : /*
      28             :  * Data Structures:
      29             :  *      buffers live in a freelist and a lookup data structure.
      30             :  *
      31             :  *
      32             :  * Buffer Lookup:
      33             :  *      Two important notes.  First, the buffer has to be
      34             :  *      available for lookup BEFORE an IO begins.  Otherwise
      35             :  *      a second process trying to read the buffer will
      36             :  *      allocate its own copy and the buffer pool will
      37             :  *      become inconsistent.
      38             :  *
      39             :  * Buffer Replacement:
      40             :  *      see freelist.c.  A buffer cannot be replaced while in
      41             :  *      use either by data manager or during IO.
      42             :  *
      43             :  *
      44             :  * Synchronization/Locking:
      45             :  *
      46             :  * IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
      47             :  *      It must be set when an IO is initiated and cleared at
      48             :  *      the end of the IO.  It is there to make sure that one
      49             :  *      process doesn't start to use a buffer while another is
      50             :  *      faulting it in.  see WaitIO and related routines.
      51             :  *
      52             :  * refcount --  Counts the number of processes holding pins on a buffer.
      53             :  *      A buffer is pinned during IO and immediately after a BufferAlloc().
      54             :  *      Pins must be released before end of transaction.  For efficiency the
      55             :  *      shared refcount isn't increased if an individual backend pins a buffer
      56             :  *      multiple times. Check the PrivateRefCount infrastructure in bufmgr.c.
      57             :  */
      58             : 
      59             : 
      60             : /*
      61             :  * Initialize shared buffer pool
      62             :  *
      63             :  * This is called once during shared-memory initialization (either in the
      64             :  * postmaster, or in a standalone backend).
      65             :  */
      66             : void
      67        1918 : BufferManagerShmemInit(void)
      68             : {
      69             :     bool        foundBufs,
      70             :                 foundDescs,
      71             :                 foundIOCV,
      72             :                 foundBufCkpt;
      73             : 
      74             :     /* Align descriptors to a cacheline boundary. */
      75        1918 :     BufferDescriptors = (BufferDescPadded *)
      76        1918 :         ShmemInitStruct("Buffer Descriptors",
      77             :                         NBuffers * sizeof(BufferDescPadded),
      78             :                         &foundDescs);
      79             : 
      80             :     /* Align buffer pool on IO page size boundary. */
      81        1918 :     BufferBlocks = (char *)
      82        1918 :         TYPEALIGN(PG_IO_ALIGN_SIZE,
      83             :                   ShmemInitStruct("Buffer Blocks",
      84             :                                   NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
      85             :                                   &foundBufs));
      86             : 
      87             :     /* Align condition variables to cacheline boundary. */
      88        1918 :     BufferIOCVArray = (ConditionVariableMinimallyPadded *)
      89        1918 :         ShmemInitStruct("Buffer IO Condition Variables",
      90             :                         NBuffers * sizeof(ConditionVariableMinimallyPadded),
      91             :                         &foundIOCV);
      92             : 
      93             :     /*
      94             :      * The array used to sort to-be-checkpointed buffer ids is located in
      95             :      * shared memory, to avoid having to allocate significant amounts of
      96             :      * memory at runtime. As that'd be in the middle of a checkpoint, or when
      97             :      * the checkpointer is restarted, memory allocation failures would be
      98             :      * painful.
      99             :      */
     100        1918 :     CkptBufferIds = (CkptSortItem *)
     101        1918 :         ShmemInitStruct("Checkpoint BufferIds",
     102             :                         NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
     103             : 
     104        1918 :     if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
     105             :     {
     106             :         /* should find all of these, or none of them */
     107             :         Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
     108             :         /* note: this path is only taken in EXEC_BACKEND case */
     109             :     }
     110             :     else
     111             :     {
     112             :         int         i;
     113             : 
     114             :         /*
     115             :          * Initialize all the buffer headers.
     116             :          */
     117    17784014 :         for (i = 0; i < NBuffers; i++)
     118             :         {
     119    17782096 :             BufferDesc *buf = GetBufferDescriptor(i);
     120             : 
     121    17782096 :             ClearBufferTag(&buf->tag);
     122             : 
     123    17782096 :             pg_atomic_init_u32(&buf->state, 0);
     124    17782096 :             buf->wait_backend_pgprocno = INVALID_PROC_NUMBER;
     125             : 
     126    17782096 :             buf->buf_id = i;
     127             : 
     128             :             /*
     129             :              * Initially link all the buffers together as unused. Subsequent
     130             :              * management of this list is done by freelist.c.
     131             :              */
     132    17782096 :             buf->freeNext = i + 1;
     133             : 
     134    17782096 :             LWLockInitialize(BufferDescriptorGetContentLock(buf),
     135             :                              LWTRANCHE_BUFFER_CONTENT);
     136             : 
     137    17782096 :             ConditionVariableInit(BufferDescriptorGetIOCV(buf));
     138             :         }
     139             : 
     140             :         /* Correct last entry of linked list */
     141        1918 :         GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
     142             :     }
     143             : 
     144             :     /* Init other shared buffer-management stuff */
     145        1918 :     StrategyInitialize(!foundDescs);
     146             : 
     147             :     /* Initialize per-backend file flush context */
     148        1918 :     WritebackContextInit(&BackendWritebackContext,
     149             :                          &backend_flush_after);
     150        1918 : }
     151             : 
     152             : /*
     153             :  * BufferManagerShmemSize
     154             :  *
     155             :  * compute the size of shared memory for the buffer pool including
     156             :  * data pages, buffer descriptors, hash tables, etc.
     157             :  */
     158             : Size
     159        3566 : BufferManagerShmemSize(void)
     160             : {
     161        3566 :     Size        size = 0;
     162             : 
     163             :     /* size of buffer descriptors */
     164        3566 :     size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
     165             :     /* to allow aligning buffer descriptors */
     166        3566 :     size = add_size(size, PG_CACHE_LINE_SIZE);
     167             : 
     168             :     /* size of data pages, plus alignment padding */
     169        3566 :     size = add_size(size, PG_IO_ALIGN_SIZE);
     170        3566 :     size = add_size(size, mul_size(NBuffers, BLCKSZ));
     171             : 
     172             :     /* size of stuff controlled by freelist.c */
     173        3566 :     size = add_size(size, StrategyShmemSize());
     174             : 
     175             :     /* size of I/O condition variables */
     176        3566 :     size = add_size(size, mul_size(NBuffers,
     177             :                                    sizeof(ConditionVariableMinimallyPadded)));
     178             :     /* to allow aligning the above */
     179        3566 :     size = add_size(size, PG_CACHE_LINE_SIZE);
     180             : 
     181             :     /* size of checkpoint sort array in bufmgr.c */
     182        3566 :     size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
     183             : 
     184        3566 :     return size;
     185             : }