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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 1.1.1.1 1996/07/09 06:21:53 scrappy 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 "storage/bufmgr.h"
#include "storage/buf_internals.h" /* where the declarations go */
#include "storage/shmem.h"
#include "storage/spin.h"
#include "utils/hsearch.h"
#include "utils/elog.h"
static HTAB *SharedBufHash;
extern HTAB *ShmemInitHash();
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 Buf 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(WARN,"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(WARN,"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(WARN,"BufTableInsert: BufferLookup table corrupted");
return(FALSE);
}
/* found something else in the table ! */
if (found) {
Assert(0);
elog(WARN,"BufTableInsert: BufferLookup table corrupted");
return(FALSE);
}
result->id = buf->buf_id;
return(TRUE);
}
/* prints out collision stats for the buf table */
void
DBG_LookupListCheck(int nlookup)
{
nlookup = 10;
hash_stats("Shared",SharedBufHash);
}
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