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Commit8a45050

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Tweak order of operations in BitmapHeapNext() to avoid the case of prefetching
the same page we are nanoseconds away from reading for real. There should besomething left to do on the current page before we consider issuing a prefetch.
1 parent405728f commit8a45050

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1 file changed

+13
-10
lines changed

1 file changed

+13
-10
lines changed

‎src/backend/executor/nodeBitmapHeapscan.c

Lines changed: 13 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -21,7 +21,7 @@
2121
*
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*
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* IDENTIFICATION
24-
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.33 2009/01/1205:10:44 tgl Exp $
24+
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.34 2009/01/1216:00:41 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -236,10 +236,22 @@ BitmapHeapNext(BitmapHeapScanState *node)
236236
#endif/* USE_PREFETCH */
237237
}
238238

239+
/*
240+
* Out of range? If so, nothing more to look at on this page
241+
*/
242+
if (scan->rs_cindex<0||scan->rs_cindex >=scan->rs_ntuples)
243+
{
244+
node->tbmres=tbmres=NULL;
245+
continue;
246+
}
247+
239248
#ifdefUSE_PREFETCH
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/*
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* We issue prefetch requests *after* fetching the current page
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* to try to avoid having prefetching interfere with the main I/O.
252+
* Also, this should happen only when we have determined there is
253+
* still something to do on the current page, else we may uselessly
254+
* prefetch the same page we are just about to request for real.
243255
*/
244256
if (prefetch_iterator)
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{
@@ -260,15 +272,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
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}
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#endif/* USE_PREFETCH */
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263-
/*
264-
* Out of range? If so, nothing more to look at on this page
265-
*/
266-
if (scan->rs_cindex<0||scan->rs_cindex >=scan->rs_ntuples)
267-
{
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node->tbmres=tbmres=NULL;
269-
continue;
270-
}
271-
272275
/*
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* Okay to fetch the tuple
274277
*/

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