Support parallel bitmap heap scans.

The index is scanned by a single process, but then all cooperating
processes can iterate jointly over the resulting set of heap blocks.
In the future, we might also want to support using a parallel bitmap
index scan to set up for a parallel bitmap heap scan, but that's a
job for another day.

Dilip Kumar, with some corrections and cosmetic 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, Thomas Munro, and me.

Discussion: http://postgr.es/m/CAFiTN-uc4=0WxRGfCzs-xfkMYcSEWUC-Fon6thkJGjkh9i=13A@mail.gmail.com

1 files changed, 57 insertions, 0 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 2fde67a9c8d..6a0d590ef29 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -26,6 +26,8 @@
 #include "utils/sortsupport.h"
 #include "utils/tuplestore.h"
 #include "utils/tuplesort.h"
+#include "nodes/tidbitmap.h"
+#include "storage/condition_variable.h"
 
 
 /* ----------------
@@ -1465,6 +1467,51 @@ typedef struct BitmapIndexScanState
 } BitmapIndexScanState;
 
 /* ----------------
+ *	 SharedBitmapState information
+ *
+ *		BM_INITIAL		TIDBitmap creation is not yet started, so first worker
+ *						to see this state will set the state to BM_INPROGRESS
+ *						and that process will be responsible for creating
+ *						TIDBitmap.
+ *		BM_INPROGRESS	TIDBitmap creation is in progress; workers need to
+ *						sleep until it's finished.
+ *		BM_FINISHED		TIDBitmap creation is done, so now all workers can
+ *						proceed to iterate over TIDBitmap.
+ * ----------------
+ */
+typedef enum
+{
+	BM_INITIAL,
+	BM_INPROGRESS,
+	BM_FINISHED
+} SharedBitmapState;
+
+/* ----------------
+ *	 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
+ *		state					current state of the TIDBitmap
+ *		cv						conditional wait variable
+ *		phs_snapshot_data		snapshot data shared to workers
+ * ----------------
+ */
+typedef struct ParallelBitmapHeapState
+{
+	dsa_pointer tbmiterator;
+	dsa_pointer prefetch_iterator;
+	slock_t		mutex;
+	int			prefetch_pages;
+	int			prefetch_target;
+	SharedBitmapState state;
+	ConditionVariable cv;
+	char		phs_snapshot_data[FLEXIBLE_ARRAY_MEMBER];
+} ParallelBitmapHeapState;
+
+/* ----------------
  *	 BitmapHeapScanState information
  *
  *		bitmapqualorig	   execution state for bitmapqualorig expressions
@@ -1477,6 +1524,11 @@ typedef struct BitmapIndexScanState
  *		prefetch_pages	   # pages prefetch iterator is ahead of current
  *		prefetch_target    current target prefetch distance
  *		prefetch_maximum   maximum value for prefetch_target
+ *		pscan_len		   size of the shared memory for parallel bitmap
+ *		initialized		   is node is ready to iterate
+ *		shared_tbmiterator	   shared iterator
+ *		shared_prefetch_iterator shared iterator for prefetching
+ *		pstate			   shared state for parallel bitmap scan
  * ----------------
  */
 typedef struct BitmapHeapScanState
@@ -1492,6 +1544,11 @@ typedef struct BitmapHeapScanState
 	int			prefetch_pages;
 	int			prefetch_target;
 	int			prefetch_maximum;
+	Size		pscan_len;
+	bool		initialized;
+	TBMSharedIterator *shared_tbmiterator;
+	TBMSharedIterator *shared_prefetch_iterator;
+	ParallelBitmapHeapState *pstate;
 } BitmapHeapScanState;
 
 /* ----------------