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Get rid of rd_nblocks field in relcache entries. Turns out this was

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costing us lots more to maintain than it was worth.  On shared tables
it was of exactly zero benefit because we couldn't trust it to be
up to date.  On temp tables it sometimes saved an lseek, but not often
enough to be worth getting excited about.  And the real problem was that
we forced an lseek on every relcache flush in order to update the field.
So all in all it seems best to lose the complexity.
This commit is contained in:
Tom Lane
2004-05-08 19:09:25 +00:00
parent 1fe11fad54
commit 4af3421161
14 changed files with 79 additions and 162 deletions
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19
src/backend/access/heap/heapam.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.165 2004/04/21 18:24:23 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.166 2004/05/08 19:09:24 tgl Exp $
*
*
* INTERFACE ROUTINES
@ -73,12 +73,13 @@ static void
initscan(HeapScanDesc scan, ScanKey key)
{
/*
* Make sure we have up-to-date idea of number of blocks in relation.
* Determine the number of blocks we have to scan.
*
* It is sufficient to do this once at scan start, since any tuples
* added while the scan is in progress will be invisible to my
* transaction anyway...
*/
scan->rs_rd->rd_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);
scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);
scan->rs_ctup.t_datamcxt = NULL;
scan->rs_ctup.t_data = NULL;
@ -113,12 +114,12 @@ heapgettup(Relation relation,
Buffer *buffer,
Snapshot snapshot,
int nkeys,
ScanKey key)
ScanKey key,
BlockNumber pages)
{
ItemId lpp;
Page dp;
BlockNumber page;
BlockNumber pages;
int lines;
OffsetNumber lineoff;
int linesleft;
@ -159,7 +160,7 @@ heapgettup(Relation relation,
/*
* return null immediately if relation is empty
*/
if ((pages = relation->rd_nblocks) == 0)
if (pages == 0)
{
if (BufferIsValid(*buffer))
ReleaseBuffer(*buffer);
@ -832,7 +833,8 @@ heap_getnext(HeapScanDesc scan, ScanDirection direction)
&(scan->rs_cbuf),
scan->rs_snapshot,
scan->rs_nkeys,
scan->rs_key);
scan->rs_key,
scan->rs_nblocks);
if (scan->rs_ctup.t_data == NULL && !BufferIsValid(scan->rs_cbuf))
{
@ -1992,7 +1994,8 @@ heap_restrpos(HeapScanDesc scan)
&(scan->rs_cbuf),
scan->rs_snapshot,
0,
NULL);
NULL,
scan->rs_nblocks);
}
}