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Avoid unnecessary lseek() calls by cleanups in md.c. mdfd_lstbcnt was

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not being consulted anywhere, so remove it and remove the _mdnblocks()
calls that were used to set it.  Change smgrextend interface to pass in
the target block number (ie, current file length) --- the caller always
knows this already, having already done smgrnblocks(), so it's silly to
do it over again inside mdextend.  Net result: extension of a file now
takes one lseek(SEEK_END) and a write(), not three lseeks and a write.
This commit is contained in:
Tom Lane
2001-05-10 20:38:49 +00:00
parent a26ad8a643
commit 642107d5ba
6 changed files with 129 additions and 106 deletions
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52
src/backend/storage/buffer/bufmgr.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.109 2001/03/22 03:59:44 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.110 2001/05/10 20:38:49 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -173,9 +173,9 @@ ReadBufferWithBufferLock(Relation reln,
bool bufferLockHeld)
{
BufferDesc *bufHdr;
int extend; /* extending the file by one block */
int status;
bool found;
bool extend; /* extending the file by one block */
bool isLocalBuf;
extend = (blockNum == P_NEW);
@ -207,21 +207,13 @@ ReadBufferWithBufferLock(Relation reln,
/* if it's already in the buffer pool, we're done */
if (found)
{
/*
* This happens when a bogus buffer was returned previously and is
* floating around in the buffer pool. A routine calling this
* would want this extended.
* Could see found && extend if a buffer was already created for
* the next page position, but then smgrextend failed to write
* the page. Must fall through and try to extend file again.
*/
if (extend)
{
/* new buffers are zero-filled */
MemSet((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
smgrextend(DEFAULT_SMGR, reln,
(char *) MAKE_PTR(bufHdr->data));
}
return BufferDescriptorGetBuffer(bufHdr);
if (!extend)
return BufferDescriptorGetBuffer(bufHdr);
}
/*
@ -232,17 +224,25 @@ ReadBufferWithBufferLock(Relation reln,
{
/* new buffers are zero-filled */
MemSet((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
status = smgrextend(DEFAULT_SMGR, reln,
status = smgrextend(DEFAULT_SMGR, reln, bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
}
else
{
status = smgrread(DEFAULT_SMGR, reln, blockNum,
status = smgrread(DEFAULT_SMGR, reln, bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
}
if (isLocalBuf)
{
/* No shared buffer state to update... */
if (status == SM_FAIL)
{
bufHdr->flags |= BM_IO_ERROR;
return InvalidBuffer;
}
return BufferDescriptorGetBuffer(bufHdr);
}
/* lock buffer manager again to update IO IN PROGRESS */
SpinAcquire(BufMgrLock);
@ -302,13 +302,11 @@ BufferAlloc(Relation reln,
*buf2;
BufferTag newTag; /* identity of requested block */
bool inProgress; /* buffer undergoing IO */
bool newblock = FALSE;
/* create a new tag so we can lookup the buffer */
/* assume that the relation is already open */
if (blockNum == P_NEW)
{
newblock = TRUE;
blockNum = smgrnblocks(DEFAULT_SMGR, reln);
}
@ -1102,7 +1100,8 @@ BufferReplace(BufferDesc *bufHdr)
/*
* RelationGetNumberOfBlocks
* Returns the buffer descriptor associated with a page in a relation.
* Determines the current number of pages in the relation.
* Side effect: relation->rd_nblocks is updated.
*
* Note:
* XXX may fail for huge relations.
@ -1112,9 +1111,16 @@ BufferReplace(BufferDesc *bufHdr)
BlockNumber
RelationGetNumberOfBlocks(Relation relation)
{
return ((relation->rd_myxactonly) ? relation->rd_nblocks :
((relation->rd_rel->relkind == RELKIND_VIEW) ? 0 :
smgrnblocks(DEFAULT_SMGR, relation)));
/*
* relation->rd_nblocks should be accurate already if the relation
* is myxactonly. (XXX how safe is that really?) Don't call smgr
* on a view, either.
*/
if (relation->rd_rel->relkind == RELKIND_VIEW)
relation->rd_nblocks = 0;
else if (!relation->rd_myxactonly)
relation->rd_nblocks = smgrnblocks(DEFAULT_SMGR, relation);
return relation->rd_nblocks;
}
/* ---------------------------------------------------------------------