From 8a4505013d9f19979fa83fced5588311d3b123d2 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 12 Jan 2009 16:00:41 +0000 Subject: [PATCH] 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 be something left to do on the current page before we consider issuing a prefetch. --- src/backend/executor/nodeBitmapHeapscan.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c index 2ba8b89ee3..b2aad2133c 100644 --- a/src/backend/executor/nodeBitmapHeapscan.c +++ b/src/backend/executor/nodeBitmapHeapscan.c @@ -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 */