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/*-------------------------------------------------------------------------
*
* buf_table.c
* routines for finding buffers in the buffer pool.
*
* NOTE: these days, what this table actually provides is a mapping from
* BufferTags to CDB indexes, not directly to buffers. The function names
* are thus slight misnomers.
*
* Note: all routines in this file assume that the BufMgrLock is held
* by the caller, so no synchronization is needed.
*
*
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.37 2004/08/29 05:06:47 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
static HTAB *SharedBufHash;
/*
* Initialize shmem hash table for mapping buffers
* size is the desired hash table size (2*NBuffers for ARC algorithm)
*/
void
InitBufTable(int size)
{
HASHCTL info;
/* assume no locking is needed yet */
/* BufferTag maps to Buffer */
info.keysize = sizeof(BufferTag);
info.entrysize = sizeof(BufferLookupEnt);
info.hash = tag_hash;
SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
size, size,
&info,
HASH_ELEM | HASH_FUNCTION);
if (!SharedBufHash)
elog(FATAL, "could not initialize shared buffer hash table");
}
/*
* BufTableLookup
* Lookup the given BufferTag; return CDB index, or -1 if not found
*/
int
BufTableLookup(BufferTag *tagPtr)
{
BufferLookupEnt *result;
if (tagPtr->blockNum == P_NEW)
return -1;
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL);
if (!result)
return -1;
return result->id;
}
/*
* BufTableInsert
* Insert a hashtable entry for given tag and CDB index
*/
void
BufTableInsert(BufferTag *tagPtr, int cdb_id)
{
BufferLookupEnt *result;
bool found;
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found);
if (!result)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of shared memory")));
if (found) /* found something else in the table? */
elog(ERROR, "shared buffer hash table corrupted");
result->id = cdb_id;
}
/*
* BufTableDelete
* Delete the hashtable entry for given tag
*/
void
BufTableDelete(BufferTag *tagPtr)
{
BufferLookupEnt *result;
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_REMOVE, NULL);
if (!result) /* shouldn't happen */
elog(ERROR, "shared buffer hash table corrupted");
}
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