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Tweak order of operations in BitmapHeapNext() to avoid the case of prefetching

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the same page we are nanoseconds away from reading for real.  There should be
something left to do on the current page before we consider issuing a prefetch.
This commit is contained in:
Tom Lane 2009-01-12 16:00:41 +00:00
parent 405728f669
commit 8a4505013d
1 changed files with 13 additions and 10 deletions
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23
src/backend/executor/nodeBitmapHeapscan.c
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@ -21,7 +21,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.33 2009/01/12 05:10:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.34 2009/01/12 16:00:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -236,10 +236,22 @@ BitmapHeapNext(BitmapHeapScanState *node)
#endif /* USE_PREFETCH */
}
/*
* Out of range? If so, nothing more to look at on this page
*/
if (scan->rs_cindex < 0 || scan->rs_cindex >= scan->rs_ntuples)
{
node->tbmres = tbmres = NULL;
continue;
}
#ifdef USE_PREFETCH
/*
* We issue prefetch requests *after* fetching the current page
* to try to avoid having prefetching interfere with the main I/O.
* Also, this should happen only when we have determined there is
* still something to do on the current page, else we may uselessly
* prefetch the same page we are just about to request for real.
*/
if (prefetch_iterator)
{
@ -260,15 +272,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
}
#endif /* USE_PREFETCH */
/*
* Out of range? If so, nothing more to look at on this page
*/
if (scan->rs_cindex < 0 || scan->rs_cindex >= scan->rs_ntuples)
{
node->tbmres = tbmres = NULL;
continue;
}
/*
* Okay to fetch the tuple
*/