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.
This commit is contained in:
Robert Haas
parent
3c3bb99330
commit
9e0fe09fc5
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@ -53,6 +53,11 @@
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static TupleTableSlot *BitmapHeapNext(BitmapHeapScanState *node);
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static void bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres);
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static inline void BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
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TBMIterateResult *tbmres);
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static inline void BitmapAdjustPrefetchTarget(BitmapHeapScanState *node);
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static inline void BitmapPrefetch(BitmapHeapScanState *node,
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HeapScanDesc scan);
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/* ----------------------------------------------------------------
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@ -69,10 +74,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
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TIDBitmap *tbm;
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TBMIterator *tbmiterator;
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TBMIterateResult *tbmres;
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#ifdef USE_PREFETCH
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TBMIterator *prefetch_iterator;
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#endif
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OffsetNumber targoffset;
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TupleTableSlot *slot;
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@ -85,9 +86,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
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tbm = node->tbm;
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tbmiterator = node->tbmiterator;
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tbmres = node->tbmres;
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#ifdef USE_PREFETCH
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prefetch_iterator = node->prefetch_iterator;
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#endif
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/*
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* If we haven't yet performed the underlying index scan, do it, and begin
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@ -115,7 +113,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
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#ifdef USE_PREFETCH
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if (node->prefetch_maximum > 0)
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{
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node->prefetch_iterator = prefetch_iterator = tbm_begin_iterate(tbm);
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node->prefetch_iterator = tbm_begin_iterate(tbm);
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node->prefetch_pages = 0;
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node->prefetch_target = -1;
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}
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@ -139,21 +137,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
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break;
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}
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#ifdef USE_PREFETCH
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if (node->prefetch_pages > 0)
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{
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/* The main iterator has closed the distance by one page */
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node->prefetch_pages--;
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}
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else if (prefetch_iterator)
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{
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/* Do not let the prefetch iterator get behind the main one */
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TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
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if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
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elog(ERROR, "prefetch and main iterators are out of sync");
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}
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#endif /* USE_PREFETCH */
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BitmapAdjustPrefetchIterator(node, tbmres);
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/*
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* Ignore any claimed entries past what we think is the end of the
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@ -182,23 +166,8 @@ BitmapHeapNext(BitmapHeapScanState *node)
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*/
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scan->rs_cindex = 0;
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#ifdef USE_PREFETCH
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/*
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* Increase prefetch target if it's not yet at the max. Note that
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* we will increase it to zero after fetching the very first
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* page/tuple, then to one after the second tuple is fetched, then
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* it doubles as later pages are fetched.
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*/
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if (node->prefetch_target >= node->prefetch_maximum)
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/* don't increase any further */ ;
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else if (node->prefetch_target >= node->prefetch_maximum / 2)
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node->prefetch_target = node->prefetch_maximum;
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else if (node->prefetch_target > 0)
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node->prefetch_target *= 2;
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else
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node->prefetch_target++;
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#endif /* USE_PREFETCH */
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/* Adjust the prefetch target */
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BitmapAdjustPrefetchTarget(node);
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}
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else
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{
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@ -227,8 +196,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
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continue;
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}
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#ifdef USE_PREFETCH
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/*
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* We issue prefetch requests *after* fetching the current page to try
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* to avoid having prefetching interfere with the main I/O. Also, this
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@ -236,24 +203,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
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* to do on the current page, else we may uselessly prefetch the same
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* page we are just about to request for real.
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*/
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if (prefetch_iterator)
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{
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while (node->prefetch_pages < node->prefetch_target)
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{
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TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
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if (tbmpre == NULL)
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{
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/* No more pages to prefetch */
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tbm_end_iterate(prefetch_iterator);
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node->prefetch_iterator = prefetch_iterator = NULL;
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break;
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}
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node->prefetch_pages++;
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PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
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}
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}
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#endif /* USE_PREFETCH */
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BitmapPrefetch(node, scan);
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/*
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* Okay to fetch the tuple
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@ -411,6 +361,84 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
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scan->rs_ntuples = ntup;
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}
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/*
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* BitmapAdjustPrefetchIterator - Adjust the prefetch iterator
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*/
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static inline void
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BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
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TBMIterateResult *tbmres)
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{
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#ifdef USE_PREFETCH
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TBMIterator *prefetch_iterator = node->prefetch_iterator;
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if (node->prefetch_pages > 0)
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{
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/* The main iterator has closed the distance by one page */
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node->prefetch_pages--;
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}
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else if (prefetch_iterator)
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{
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/* Do not let the prefetch iterator get behind the main one */
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TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
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if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
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elog(ERROR, "prefetch and main iterators are out of sync");
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}
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#endif /* USE_PREFETCH */
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}
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/*
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* BitmapAdjustPrefetchTarget - Adjust the prefetch target
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*
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* Increase prefetch target if it's not yet at the max. Note that
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* we will increase it to zero after fetching the very first
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* page/tuple, then to one after the second tuple is fetched, then
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* it doubles as later pages are fetched.
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*/
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static inline void
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BitmapAdjustPrefetchTarget(BitmapHeapScanState *node)
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{
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#ifdef USE_PREFETCH
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if (node->prefetch_target >= node->prefetch_maximum)
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/* don't increase any further */ ;
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else if (node->prefetch_target >= node->prefetch_maximum / 2)
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node->prefetch_target = node->prefetch_maximum;
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else if (node->prefetch_target > 0)
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node->prefetch_target *= 2;
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else
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node->prefetch_target++;
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#endif /* USE_PREFETCH */
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}
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/*
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* BitmapPrefetch - Prefetch, if prefetch_pages are behind prefetch_target
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*/
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static inline void
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BitmapPrefetch(BitmapHeapScanState *node, HeapScanDesc scan)
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{
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#ifdef USE_PREFETCH
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TBMIterator *prefetch_iterator = node->prefetch_iterator;
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if (prefetch_iterator)
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{
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while (node->prefetch_pages < node->prefetch_target)
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{
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TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
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if (tbmpre == NULL)
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{
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/* No more pages to prefetch */
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tbm_end_iterate(prefetch_iterator);
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node->prefetch_iterator = NULL;
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break;
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}
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node->prefetch_pages++;
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PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
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}
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}
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#endif /* USE_PREFETCH */
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}
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/*
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* BitmapHeapRecheck -- access method routine to recheck a tuple in EvalPlanQual
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*/
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