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Split the buffer mapping table into multiple separately lockable

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partitions, as per discussion.  Passes functionality checks, but
I don't have any performance data yet.
This commit is contained in:
Tom Lane
2006-07-23 03:07:58 +00:00
parent 51ee9fa157
commit 10b9ca3d05
8 changed files with 198 additions and 75 deletions
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56
src/backend/storage/buffer/buf_table.c
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@ -4,8 +4,10 @@
* routines for mapping BufferTags to buffer indexes.
*
* 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.
* must hold a suitable lock on the appropriate BufMappingLock, as specified
* in the comments. We can't do the locking inside these functions because
* in most cases the caller needs to adjust the buffer header contents
* before the lock is released (see notes in README).
*
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
@ -13,7 +15,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.46 2006/07/14 16:59:19 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.47 2006/07/23 03:07:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -58,29 +60,49 @@ InitBufTable(int size)
info.keysize = sizeof(BufferTag);
info.entrysize = sizeof(BufferLookupEnt);
info.hash = tag_hash;
info.num_partitions = NUM_BUFFER_PARTITIONS;
SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
size, size,
&info,
HASH_ELEM | HASH_FUNCTION);
HASH_ELEM | HASH_FUNCTION | HASH_PARTITION);
if (!SharedBufHash)
elog(FATAL, "could not initialize shared buffer hash table");
}
/*
* BufTableHashCode
* Compute the hash code associated with a BufferTag
*
* This must be passed to the lookup/insert/delete routines along with the
* tag. We do it like this because the callers need to know the hash code
* in order to determine which buffer partition to lock, and we don't want
* to do the hash computation twice (hash_any is a bit slow).
*/
uint32
BufTableHashCode(BufferTag *tagPtr)
{
return get_hash_value(SharedBufHash, (void *) tagPtr);
}
/*
* BufTableLookup
* Lookup the given BufferTag; return buffer ID, or -1 if not found
*
* Caller must hold at least share lock on BufMappingLock
* Caller must hold at least share lock on BufMappingLock for tag's partition
*/
int
BufTableLookup(BufferTag *tagPtr)
BufTableLookup(BufferTag *tagPtr, uint32 hashcode)
{
BufferLookupEnt *result;
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL);
hash_search_with_hash_value(SharedBufHash,
(void *) tagPtr,
hashcode,
HASH_FIND,
NULL);
if (!result)
return -1;
@ -96,10 +118,10 @@ BufTableLookup(BufferTag *tagPtr)
* 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
* Caller must hold exclusive lock on BufMappingLock for tag's partition
*/
int
BufTableInsert(BufferTag *tagPtr, int buf_id)
BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id)
{
BufferLookupEnt *result;
bool found;
@ -108,7 +130,11 @@ BufTableInsert(BufferTag *tagPtr, int buf_id)
Assert(tagPtr->blockNum != P_NEW); /* invalid tag */
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found);
hash_search_with_hash_value(SharedBufHash,
(void *) tagPtr,
hashcode,
HASH_ENTER,
&found);
if (found) /* found something already in the table */
return result->id;
@ -122,15 +148,19 @@ BufTableInsert(BufferTag *tagPtr, int buf_id)
* BufTableDelete
* Delete the hashtable entry for given tag (which must exist)
*
* Caller must hold write lock on BufMappingLock
* Caller must hold exclusive lock on BufMappingLock for tag's partition
*/
void
BufTableDelete(BufferTag *tagPtr)
BufTableDelete(BufferTag *tagPtr, uint32 hashcode)
{
BufferLookupEnt *result;
result = (BufferLookupEnt *)
hash_search(SharedBufHash, (void *) tagPtr, HASH_REMOVE, NULL);
hash_search_with_hash_value(SharedBufHash,
(void *) tagPtr,
hashcode,
HASH_REMOVE,
NULL);
if (!result) /* shouldn't happen */
elog(ERROR, "shared buffer hash table corrupted");