@ -21,7 +21,7 @@
*
*
* IDENTIFICATION
* $ PostgreSQL : pgsql / src / backend / executor / nodeBitmapHeapscan . c , v 1.32 2009 / 01 / 10 21 : 08 : 36 tgl Exp $
* $ PostgreSQL : pgsql / src / backend / executor / nodeBitmapHeapscan . c , v 1.33 2009 / 01 / 12 05 : 10 : 44 tgl Exp $
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
@ -67,6 +67,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
TIDBitmap * tbm ;
TBMIterator * tbmiterator ;
TBMIterateResult * tbmres ;
TBMIterator * prefetch_iterator ;
OffsetNumber targoffset ;
TupleTableSlot * slot ;
@ -81,6 +82,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
tbm = node - > tbm ;
tbmiterator = node - > tbmiterator ;
tbmres = node - > tbmres ;
prefetch_iterator = node - > prefetch_iterator ;
/*
* Check if we are evaluating PlanQual for tuple of this relation .
@ -114,6 +116,15 @@ BitmapHeapNext(BitmapHeapScanState *node)
/*
* If we haven ' t yet performed the underlying index scan , do it , and
* begin the iteration over the bitmap .
*
* For prefetching , we use * two * iterators , one for the pages we are
* actually scanning and another that runs ahead of the first for
* prefetching . node - > prefetch_pages tracks exactly how many pages
* ahead the prefetch iterator is . Also , node - > prefetch_target tracks
* the desired prefetch distance , which starts small and increases up
* to the GUC - controlled maximum , target_prefetch_pages . This is to
* avoid doing a lot of prefetching in a scan that stops after a few
* tuples because of a LIMIT .
*/
if ( tbm = = NULL )
{
@ -125,6 +136,15 @@ BitmapHeapNext(BitmapHeapScanState *node)
node - > tbm = tbm ;
node - > tbmiterator = tbmiterator = tbm_begin_iterate ( tbm ) ;
node - > tbmres = tbmres = NULL ;
# ifdef USE_PREFETCH
if ( target_prefetch_pages > 0 )
{
node - > prefetch_iterator = prefetch_iterator = tbm_begin_iterate ( tbm ) ;
node - > prefetch_pages = 0 ;
node - > prefetch_target = - 1 ;
}
# endif /* USE_PREFETCH */
}
for ( ; ; )
@ -144,6 +164,22 @@ BitmapHeapNext(BitmapHeapScanState *node)
break ;
}
# ifdef USE_PREFETCH
if ( node - > prefetch_pages > 0 )
{
/* The main iterator has closed the distance by one page */
node - > prefetch_pages - - ;
}
else if ( prefetch_iterator )
{
/* Do not let the prefetch iterator get behind the main one */
TBMIterateResult * tbmpre = tbm_iterate ( prefetch_iterator ) ;
if ( tbmpre = = NULL | | tbmpre - > blockno ! = tbmres - > blockno )
elog ( ERROR , " prefetch and main iterators are out of sync " ) ;
}
# endif /* USE_PREFETCH */
/*
* Ignore any claimed entries past what we think is the end of the
* relation . ( This is probably not necessary given that we got at
@ -165,6 +201,23 @@ BitmapHeapNext(BitmapHeapScanState *node)
* Set rs_cindex to first slot to examine
*/
scan - > rs_cindex = 0 ;
# ifdef USE_PREFETCH
/*
* Increase prefetch target if it ' s not yet at the max . Note
* that we will increase it to zero after fetching the very
* first page / tuple , then to one after the second tuple is
* fetched , then it doubles as later pages are fetched .
*/
if ( node - > prefetch_target > = target_prefetch_pages )
/* don't increase any further */ ;
else if ( node - > prefetch_target > = target_prefetch_pages / 2 )
node - > prefetch_target = target_prefetch_pages ;
else if ( node - > prefetch_target > 0 )
node - > prefetch_target * = 2 ;
else
node - > prefetch_target + + ;
# endif /* USE_PREFETCH */
}
else
{
@ -172,7 +225,40 @@ BitmapHeapNext(BitmapHeapScanState *node)
* Continuing in previously obtained page ; advance rs_cindex
*/
scan - > rs_cindex + + ;
# ifdef USE_PREFETCH
/*
* Try to prefetch at least a few pages even before we get to the
* second page if we don ' t stop reading after the first tuple .
*/
if ( node - > prefetch_target < target_prefetch_pages )
node - > prefetch_target + + ;
# endif /* USE_PREFETCH */
}
# ifdef USE_PREFETCH
/*
* We issue prefetch requests * after * fetching the current page
* to try to avoid having prefetching interfere with the main I / O .
*/
if ( prefetch_iterator )
{
while ( node - > prefetch_pages < node - > prefetch_target )
{
TBMIterateResult * tbmpre = tbm_iterate ( prefetch_iterator ) ;
if ( tbmpre = = NULL )
{
/* No more pages to prefetch */
tbm_end_iterate ( prefetch_iterator ) ;
node - > prefetch_iterator = prefetch_iterator = NULL ;
break ;
}
node - > prefetch_pages + + ;
PrefetchBuffer ( scan - > rs_rd , MAIN_FORKNUM , tbmpre - > blockno ) ;
}
}
# endif /* USE_PREFETCH */
/*
* Out of range ? If so , nothing more to look at on this page
@ -379,11 +465,14 @@ ExecBitmapHeapReScan(BitmapHeapScanState *node, ExprContext *exprCtxt)
if ( node - > tbmiterator )
tbm_end_iterate ( node - > tbmiterator ) ;
if ( node - > prefetch_iterator )
tbm_end_iterate ( node - > prefetch_iterator ) ;
if ( node - > tbm )
tbm_free ( node - > tbm ) ;
node - > tbm = NULL ;
node - > tbmiterator = NULL ;
node - > tbmres = NULL ;
node - > prefetch_iterator = NULL ;
/*
* Always rescan the input immediately , to ensure we can pass down any
@ -429,6 +518,8 @@ ExecEndBitmapHeapScan(BitmapHeapScanState *node)
*/
if ( node - > tbmiterator )
tbm_end_iterate ( node - > tbmiterator ) ;
if ( node - > prefetch_iterator )
tbm_end_iterate ( node - > prefetch_iterator ) ;
if ( node - > tbm )
tbm_free ( node - > tbm ) ;
@ -474,6 +565,9 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
scanstate - > tbm = NULL ;
scanstate - > tbmiterator = NULL ;
scanstate - > tbmres = NULL ;
scanstate - > prefetch_iterator = NULL ;
scanstate - > prefetch_pages = 0 ;
scanstate - > prefetch_target = 0 ;
/*
* Miscellaneous initialization
Tom Lane
17 years ago