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Replace the BufMgrLock with separate locks on the lookup hashtable and

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the freelist, plus per-buffer spinlocks that protect access to individual
shared buffer headers.  This requires abandoning a global freelist (since
the freelist is a global contention point), which shoots down ARC and 2Q
as well as plain LRU management.  Adopt a clock sweep algorithm instead.
Preliminary results show substantial improvement in multi-backend situations.
This commit is contained in:
Tom Lane
2005-03-04 20:21:07 +00:00
parent 5592a6cf46
commit 5d5087363d
18 changed files with 1410 additions and 1932 deletions
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38
src/backend/storage/buffer/buf_table.c
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@ -3,12 +3,9 @@
* buf_table.c
* routines for mapping BufferTags to buffer indexes.
*
* NOTE: this module is called only by freelist.c, and the "buffer IDs"
* it deals with are whatever freelist.c needs them to be; they may not be
* directly equivalent to Buffer numbers.
*
* Note: all routines in this file assume that the BufMgrLock is held
* by the caller, so no synchronization is needed.
* Note: the routines in this file do no locking of their own. The caller
* must hold a suitable lock on the BufMappingLock, as specified in the
* comments.
*
*
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
@ -16,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.39 2005/02/03 23:29:11 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.40 2005/03/04 20:21:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -74,17 +71,17 @@ InitBufTable(int size)
/*
* BufTableLookup
* Lookup the given BufferTag; return buffer ID, or -1 if not found
*
* Caller must hold at least share lock on BufMappingLock
*/
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;
@ -93,14 +90,23 @@ BufTableLookup(BufferTag *tagPtr)
/*
* BufTableInsert
* Insert a hashtable entry for given tag and buffer ID
* Insert a hashtable entry for given tag and buffer ID,
* unless an entry already exists for that tag
*
* Returns -1 on successful insertion. If a conflicting entry exists
* already, returns the buffer ID in that entry.
*
* Caller must hold write lock on BufMappingLock
*/
void
int
BufTableInsert(BufferTag *tagPtr, int buf_id)
{
BufferLookupEnt *result;
bool found;
Assert(buf_id >= 0); /* -1 is reserved for not-in-table */
Assert(tagPtr->blockNum != P_NEW); /* invalid tag */
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found);
@ -109,15 +115,19 @@ BufTableInsert(BufferTag *tagPtr, int buf_id)
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of shared memory")));
if (found) /* found something already in the table? */
elog(ERROR, "shared buffer hash table corrupted");
if (found) /* found something already in the table */
return result->id;
result->id = buf_id;
return -1;
}
/*
* BufTableDelete
* Delete the hashtable entry for given tag (which must exist)
*
* Caller must hold write lock on BufMappingLock
*/
void
BufTableDelete(BufferTag *tagPtr)