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robertmhaasrobertmhaas
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Refactor bitmap heap scan in preparation for parallel support.
The final patch will be less messy if the prefetching support is a bit better isolated, so do that. Dilip Kumar, with some changes by me. The larger patch set of which this is a part has been reviewed and tested by (at least) Andres Freund, Amit Khandekar, Tushar Ahuja, Rafia Sabih, Haribabu Kommi, and Thomas Munro.
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‎src/backend/executor/nodeBitmapHeapscan.c

Lines changed: 88 additions & 60 deletions
Original file line numberDiff line numberDiff line change
@@ -53,6 +53,11 @@
5353

5454
static TupleTableSlot *BitmapHeapNext(BitmapHeapScanState *node);
5555
static void bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres);
56+
static inline void BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
57+
TBMIterateResult *tbmres);
58+
static inline void BitmapAdjustPrefetchTarget(BitmapHeapScanState *node);
59+
static inline void BitmapPrefetch(BitmapHeapScanState *node,
60+
HeapScanDesc scan);
5661

5762

5863
/* ----------------------------------------------------------------
@@ -69,10 +74,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
6974
TIDBitmap *tbm;
7075
TBMIterator *tbmiterator;
7176
TBMIterateResult *tbmres;
72-
73-
#ifdef USE_PREFETCH
74-
TBMIterator *prefetch_iterator;
75-
#endif
7677
OffsetNumber targoffset;
7778
TupleTableSlot *slot;
7879

@@ -85,9 +86,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
8586
tbm = node->tbm;
8687
tbmiterator = node->tbmiterator;
8788
tbmres = node->tbmres;
88-
#ifdef USE_PREFETCH
89-
prefetch_iterator = node->prefetch_iterator;
90-
#endif
9189

9290
/*
9391
* If we haven't yet performed the underlying index scan, do it, and begin
@@ -115,7 +113,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
115113
#ifdef USE_PREFETCH
116114
if (node->prefetch_maximum > 0)
117115
{
118-
node->prefetch_iterator = prefetch_iterator = tbm_begin_iterate(tbm);
116+
node->prefetch_iterator = tbm_begin_iterate(tbm);
119117
node->prefetch_pages = 0;
120118
node->prefetch_target = -1;
121119
}
@@ -139,21 +137,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
139137
break;
140138
}
141139

142-
#ifdef USE_PREFETCH
143-
if (node->prefetch_pages > 0)
144-
{
145-
/* The main iterator has closed the distance by one page */
146-
node->prefetch_pages--;
147-
}
148-
else if (prefetch_iterator)
149-
{
150-
/* Do not let the prefetch iterator get behind the main one */
151-
TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
152-
153-
if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
154-
elog(ERROR, "prefetch and main iterators are out of sync");
155-
}
156-
#endif /* USE_PREFETCH */
140+
BitmapAdjustPrefetchIterator(node, tbmres);
157141

158142
/*
159143
* Ignore any claimed entries past what we think is the end of the
@@ -182,23 +166,8 @@ BitmapHeapNext(BitmapHeapScanState *node)
182166
*/
183167
scan->rs_cindex = 0;
184168

185-
#ifdef USE_PREFETCH
186-
187-
/*
188-
* Increase prefetch target if it's not yet at the max. Note that
189-
* we will increase it to zero after fetching the very first
190-
* page/tuple, then to one after the second tuple is fetched, then
191-
* it doubles as later pages are fetched.
192-
*/
193-
if (node->prefetch_target >= node->prefetch_maximum)
194-
/* don't increase any further */ ;
195-
else if (node->prefetch_target >= node->prefetch_maximum / 2)
196-
node->prefetch_target = node->prefetch_maximum;
197-
else if (node->prefetch_target > 0)
198-
node->prefetch_target *= 2;
199-
else
200-
node->prefetch_target++;
201-
#endif /* USE_PREFETCH */
169+
/* Adjust the prefetch target */
170+
BitmapAdjustPrefetchTarget(node);
202171
}
203172
else
204173
{
@@ -227,33 +196,14 @@ BitmapHeapNext(BitmapHeapScanState *node)
227196
continue;
228197
}
229198

230-
#ifdef USE_PREFETCH
231-
232199
/*
233200
* We issue prefetch requests *after* fetching the current page to try
234201
* to avoid having prefetching interfere with the main I/O. Also, this
235202
* should happen only when we have determined there is still something
236203
* to do on the current page, else we may uselessly prefetch the same
237204
* page we are just about to request for real.
238205
*/
239-
if (prefetch_iterator)
240-
{
241-
while (node->prefetch_pages < node->prefetch_target)
242-
{
243-
TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
244-
245-
if (tbmpre == NULL)
246-
{
247-
/* No more pages to prefetch */
248-
tbm_end_iterate(prefetch_iterator);
249-
node->prefetch_iterator = prefetch_iterator = NULL;
250-
break;
251-
}
252-
node->prefetch_pages++;
253-
PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
254-
}
255-
}
256-
#endif /* USE_PREFETCH */
206+
BitmapPrefetch(node, scan);
257207

258208
/*
259209
* Okay to fetch the tuple
@@ -411,6 +361,84 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
411361
scan->rs_ntuples = ntup;
412362
}
413363

364+
/*
365+
* BitmapAdjustPrefetchIterator - Adjust the prefetch iterator
366+
*/
367+
static inline void
368+
BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
369+
TBMIterateResult *tbmres)
370+
{
371+
#ifdef USE_PREFETCH
372+
TBMIterator *prefetch_iterator = node->prefetch_iterator;
373+
374+
if (node->prefetch_pages > 0)
375+
{
376+
/* The main iterator has closed the distance by one page */
377+
node->prefetch_pages--;
378+
}
379+
else if (prefetch_iterator)
380+
{
381+
/* Do not let the prefetch iterator get behind the main one */
382+
TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
383+
384+
if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
385+
elog(ERROR, "prefetch and main iterators are out of sync");
386+
}
387+
#endif /* USE_PREFETCH */
388+
}
389+
390+
/*
391+
* BitmapAdjustPrefetchTarget - Adjust the prefetch target
392+
*
393+
* Increase prefetch target if it's not yet at the max. Note that
394+
* we will increase it to zero after fetching the very first
395+
* page/tuple, then to one after the second tuple is fetched, then
396+
* it doubles as later pages are fetched.
397+
*/
398+
static inline void
399+
BitmapAdjustPrefetchTarget(BitmapHeapScanState *node)
400+
{
401+
#ifdef USE_PREFETCH
402+
if (node->prefetch_target >= node->prefetch_maximum)
403+
/* don't increase any further */ ;
404+
else if (node->prefetch_target >= node->prefetch_maximum / 2)
405+
node->prefetch_target = node->prefetch_maximum;
406+
else if (node->prefetch_target > 0)
407+
node->prefetch_target *= 2;
408+
else
409+
node->prefetch_target++;
410+
#endif /* USE_PREFETCH */
411+
}
412+
413+
/*
414+
* BitmapPrefetch - Prefetch, if prefetch_pages are behind prefetch_target
415+
*/
416+
static inline void
417+
BitmapPrefetch(BitmapHeapScanState *node, HeapScanDesc scan)
418+
{
419+
#ifdef USE_PREFETCH
420+
TBMIterator *prefetch_iterator = node->prefetch_iterator;
421+
422+
if (prefetch_iterator)
423+
{
424+
while (node->prefetch_pages < node->prefetch_target)
425+
{
426+
TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
427+
428+
if (tbmpre == NULL)
429+
{
430+
/* No more pages to prefetch */
431+
tbm_end_iterate(prefetch_iterator);
432+
node->prefetch_iterator = NULL;
433+
break;
434+
}
435+
node->prefetch_pages++;
436+
PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
437+
}
438+
}
439+
#endif /* USE_PREFETCH */
440+
}
441+
414442
/*
415443
* BitmapHeapRecheck -- access method routine to recheck a tuple in EvalPlanQual
416444
*/

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