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/*-------------------------------------------------------------------------
*
* buf_table.c
* routines for finding buffers in the buffer pool.
*
* Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_table.c,v 1.14 1999/02/13 23:17:55 momjian Exp $
*
*-------------------------------------------------------------------------
*/
/*
* OLD COMMENTS
*
* Data Structures:
*
* Buffers are identified by their BufferTag (buf.h). This
* file contains routines for allocating a shmem hash table to
* map buffer tags to buffer descriptors.
*
* Synchronization:
*
* All routines in this file assume buffer manager spinlock is
* held by their caller.
*/
#include "postgres.h"
#include "storage/bufmgr.h"
#include "storage/buf_internals.h" /* where the declarations go */
#include "storage/shmem.h"
#include "storage/spin.h"
#include "utils/hsearch.h"
static HTAB *SharedBufHash;
typedef struct lookup
{
BufferTag key;
Buffer id;
} LookupEnt;
/*
* Initialize shmem hash table for mapping buffers
*/
void
InitBufTable()
{
HASHCTL info;
int hash_flags;
/* assume lock is held */
/* BufferTag maps to Buffer */
info.keysize = sizeof(BufferTag);
info.datasize = sizeof(Buffer);
info.hash = tag_hash;
hash_flags = (HASH_ELEM | HASH_FUNCTION);
SharedBufHash = (HTAB *) ShmemInitHash("Shared Buffer Lookup Table",
NBuffers, NBuffers,
&info, hash_flags);
if (!SharedBufHash)
{
elog(FATAL, "couldn't initialize shared buffer pool Hash Tbl");
exit(1);
}
}
BufferDesc *
BufTableLookup(BufferTag *tagPtr)
{
LookupEnt *result;
bool found;
if (tagPtr->blockNum == P_NEW)
return NULL;
result = (LookupEnt *)
hash_search(SharedBufHash, (char *) tagPtr, HASH_FIND, &found);
if (!result)
{
elog(ERROR, "BufTableLookup: BufferLookup table corrupted");
return NULL;
}
if (!found)
return NULL;
return &(BufferDescriptors[result->id]);
}
/*
* BufTableDelete
*/
bool
BufTableDelete(BufferDesc *buf)
{
LookupEnt *result;
bool found;
/*
* buffer not initialized or has been removed from table already.
* BM_DELETED keeps us from removing buffer twice.
*/
if (buf->flags & BM_DELETED)
return TRUE;
buf->flags |= BM_DELETED;
result = (LookupEnt *)
hash_search(SharedBufHash, (char *) &(buf->tag), HASH_REMOVE, &found);
if (!(result && found))
{
elog(ERROR, "BufTableDelete: BufferLookup table corrupted");
return FALSE;
}
return TRUE;
}
bool
BufTableInsert(BufferDesc *buf)
{
LookupEnt *result;
bool found;
/* cannot insert it twice */
Assert(buf->flags & BM_DELETED);
buf->flags &= ~(BM_DELETED);
result = (LookupEnt *)
hash_search(SharedBufHash, (char *) &(buf->tag), HASH_ENTER, &found);
if (!result)
{
Assert(0);
elog(ERROR, "BufTableInsert: BufferLookup table corrupted");
return FALSE;
}
/* found something else in the table ! */
if (found)
{
Assert(0);
elog(ERROR, "BufTableInsert: BufferLookup table corrupted");
return FALSE;
}
result->id = buf->buf_id;
return TRUE;
}
/* prints out collision stats for the buf table */
#ifdef NOT_USED
void
DBG_LookupListCheck(int nlookup)
{
nlookup = 10;
hash_stats("Shared", SharedBufHash);
}
#endif
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