BitmapHeapScan uses the read stream API

Make Bitmap Heap Scan use the read stream API instead of invoking
ReadBuffer() for each block indicated by the bitmap.

The read stream API handles prefetching, so remove all of the explicit
prefetching from bitmap heap scan code.

Now, heap table AM implements a read stream callback which uses the
bitmap iterator to return the next required block to the read stream
code.

Tomas Vondra conducted extensive regression testing of this feature.
Andres Freund, Thomas Munro, and I analyzed regressions and Thomas Munro
patched the read stream API.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Tested-by: Tomas Vondra <tomas@vondra.me>
Tested-by: Andres Freund <andres@anarazel.de>
Tested-by: Thomas Munro <thomas.munro@gmail.com>
Tested-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/flat/CAAKRu_ZwCwWFeL_H3ia26bP2e7HiKLWt0ZmGXPVwPO6uXq0vaA%40mail.gmail.com

1 files changed, 1 insertions, 22 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 575b0b1bd24..d4d4e655180 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1840,11 +1840,7 @@ typedef enum
 /* ----------------
  *	 ParallelBitmapHeapState information
  *		tbmiterator				iterator for scanning current pages
- *		prefetch_iterator		iterator for prefetching ahead of current page
- *		mutex					mutual exclusion for the prefetching variable
- *								and state
- *		prefetch_pages			# pages prefetch iterator is ahead of current
- *		prefetch_target			current target prefetch distance
+ *		mutex					mutual exclusion for state
  *		state					current state of the TIDBitmap
  *		cv						conditional wait variable
  * ----------------
@@ -1852,10 +1848,7 @@ typedef enum
 typedef struct ParallelBitmapHeapState
 {
 	dsa_pointer tbmiterator;
-	dsa_pointer prefetch_iterator;
 	slock_t		mutex;
-	int			prefetch_pages;
-	int			prefetch_target;
 	SharedBitmapState state;
 	ConditionVariable cv;
 } ParallelBitmapHeapState;
@@ -1879,18 +1872,11 @@ typedef struct SharedBitmapHeapInstrumentation
  *
  *		bitmapqualorig	   execution state for bitmapqualorig expressions
  *		tbm				   bitmap obtained from child index scan(s)
- *		pvmbuffer		   buffer for visibility-map lookups of prefetched pages
  *		stats			   execution statistics
- *		prefetch_iterator  iterator for prefetching ahead of current page
- *		prefetch_pages	   # pages prefetch iterator is ahead of current
- *		prefetch_target    current target prefetch distance
- *		prefetch_maximum   maximum value for prefetch_target
  *		initialized		   is node is ready to iterate
  *		pstate			   shared state for parallel bitmap scan
  *		sinstrument		   statistics for parallel workers
  *		recheck			   do current page's tuples need recheck
- *		blockno			   used to validate pf and current block stay in sync
- *		prefetch_blockno   used to validate pf stays ahead of current block
  * ----------------
  */
 typedef struct BitmapHeapScanState
@@ -1898,18 +1884,11 @@ typedef struct BitmapHeapScanState
 	ScanState	ss;				/* its first field is NodeTag */
 	ExprState  *bitmapqualorig;
 	TIDBitmap  *tbm;
-	Buffer		pvmbuffer;
 	BitmapHeapScanInstrumentation stats;
-	TBMIterator prefetch_iterator;
-	int			prefetch_pages;
-	int			prefetch_target;
-	int			prefetch_maximum;
 	bool		initialized;
 	ParallelBitmapHeapState *pstate;
 	SharedBitmapHeapInstrumentation *sinstrument;
 	bool		recheck;
-	BlockNumber blockno;
-	BlockNumber prefetch_blockno;
 } BitmapHeapScanState;
 
 /* ----------------