Add optimizer and executor support for parallel index scans.

In combination with 569174f1be92be93f5366212cc46960d28a5c5cd, which
taught the btree AM how to perform parallel index scans, this allows
parallel index scan plans on btree indexes.  This infrastructure
should be general enough to support parallel index scans for other
index AMs as well, if someone updates them to support parallel
scans.

Amit Kapila, reviewed and tested by Anastasia Lubennikova, Tushar
Ahuja, and Haribabu Kommi, and me.

8 files changed, 28 insertions, 9 deletions

diff --git a/src/include/access/amapi.h b/src/include/access/amapi.h
index b0730bfefae..f919cf8b873 100644
--- a/src/include/access/amapi.h
+++ b/src/include/access/amapi.h
@@ -95,7 +95,8 @@ typedef void (*amcostestimate_function) (struct PlannerInfo *root,
 													 Cost *indexStartupCost,
 													 Cost *indexTotalCost,
 											   Selectivity *indexSelectivity,
-												   double *indexCorrelation);
+													 double *indexCorrelation,
+													 double *indexPages);
 
 /* parse index reloptions */
 typedef bytea *(*amoptions_function) (Datum reloptions,
@@ -188,6 +189,8 @@ typedef struct IndexAmRoutine
 	bool		amclusterable;
 	/* does AM handle predicate locks? */
 	bool		ampredlocks;
+	/* does AM support parallel scan? */
+	bool		amcanparallel;
 	/* type of data stored in index, or InvalidOid if variable */
 	Oid			amkeytype;
 
diff --git a/src/include/executor/nodeIndexscan.h b/src/include/executor/nodeIndexscan.h
index 46d6f45e837..ea3f3a5cc4d 100644
--- a/src/include/executor/nodeIndexscan.h
+++ b/src/include/executor/nodeIndexscan.h
@@ -14,6 +14,7 @@
 #ifndef NODEINDEXSCAN_H
 #define NODEINDEXSCAN_H
 
+#include "access/parallel.h"
 #include "nodes/execnodes.h"
 
 extern IndexScanState *ExecInitIndexScan(IndexScan *node, EState *estate, int eflags);
@@ -22,6 +23,9 @@ extern void ExecEndIndexScan(IndexScanState *node);
 extern void ExecIndexMarkPos(IndexScanState *node);
 extern void ExecIndexRestrPos(IndexScanState *node);
 extern void ExecReScanIndexScan(IndexScanState *node);
+extern void ExecIndexScanEstimate(IndexScanState *node, ParallelContext *pcxt);
+extern void ExecIndexScanInitializeDSM(IndexScanState *node, ParallelContext *pcxt);
+extern void ExecIndexScanInitializeWorker(IndexScanState *node, shm_toc *toc);
 
 /*
  * These routines are exported to share code with nodeIndexonlyscan.c and
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 42c6c58ff9c..9f41babf353 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1363,6 +1363,7 @@ typedef struct
  *		SortSupport		   for reordering ORDER BY exprs
  *		OrderByTypByVals   is the datatype of order by expression pass-by-value?
  *		OrderByTypLens	   typlens of the datatypes of order by expressions
+ *		pscan_len		   size of parallel index scan descriptor
  * ----------------
  */
 typedef struct IndexScanState
@@ -1389,6 +1390,7 @@ typedef struct IndexScanState
 	SortSupport iss_SortSupport;
 	bool	   *iss_OrderByTypByVals;
 	int16	   *iss_OrderByTypLens;
+	Size		iss_PscanLen;
 } IndexScanState;
 
 /* ----------------
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 643be54d405..f7ac6f600fe 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -629,6 +629,7 @@ typedef struct IndexOptInfo
 	bool		amsearchnulls;	/* can AM search for NULL/NOT NULL entries? */
 	bool		amhasgettuple;	/* does AM have amgettuple interface? */
 	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
+	bool		amcanparallel;	/* does AM support parallel scan? */
 	/* Rather than include amapi.h here, we declare amcostestimate like this */
 	void		(*amcostestimate) ();	/* AM's cost estimator */
 } IndexOptInfo;
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index 0e68264a41f..72200fa5310 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -76,7 +76,7 @@ extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
 extern void cost_samplescan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
 				ParamPathInfo *param_info);
 extern void cost_index(IndexPath *path, PlannerInfo *root,
-		   double loop_count);
+		   double loop_count, bool partial_path);
 extern void cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
 					  ParamPathInfo *param_info,
 					  Path *bitmapqual, double loop_count);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 7b413176219..53cad247dc4 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -47,7 +47,8 @@ extern IndexPath *create_index_path(PlannerInfo *root,
 				  ScanDirection indexscandir,
 				  bool indexonly,
 				  Relids required_outer,
-				  double loop_count);
+				  double loop_count,
+				  bool partial_path);
 extern BitmapHeapPath *create_bitmap_heap_path(PlannerInfo *root,
 						RelOptInfo *rel,
 						Path *bitmapqual,
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 81e7a4274da..ebda308c416 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -54,6 +54,8 @@ extern RelOptInfo *standard_join_search(PlannerInfo *root, int levels_needed,
 					 List *initial_rels);
 
 extern void generate_gather_paths(PlannerInfo *root, RelOptInfo *rel);
+extern int compute_parallel_worker(RelOptInfo *rel, BlockNumber heap_pages,
+						BlockNumber index_pages);
 
 #ifdef OPTIMIZER_DEBUG
 extern void debug_print_rel(PlannerInfo *root, RelOptInfo *rel);
diff --git a/src/include/utils/index_selfuncs.h b/src/include/utils/index_selfuncs.h
index d3172420f99..17d165ca651 100644
--- a/src/include/utils/index_selfuncs.h
+++ b/src/include/utils/index_selfuncs.h
@@ -28,41 +28,47 @@ extern void brincostestimate(struct PlannerInfo *root,
 				 Cost *indexStartupCost,
 				 Cost *indexTotalCost,
 				 Selectivity *indexSelectivity,
-				 double *indexCorrelation);
+				 double *indexCorrelation,
+				 double *indexPages);
 extern void btcostestimate(struct PlannerInfo *root,
 			   struct IndexPath *path,
 			   double loop_count,
 			   Cost *indexStartupCost,
 			   Cost *indexTotalCost,
 			   Selectivity *indexSelectivity,
-			   double *indexCorrelation);
+			   double *indexCorrelation,
+			   double *indexPages);
 extern void hashcostestimate(struct PlannerInfo *root,
 				 struct IndexPath *path,
 				 double loop_count,
 				 Cost *indexStartupCost,
 				 Cost *indexTotalCost,
 				 Selectivity *indexSelectivity,
-				 double *indexCorrelation);
+				 double *indexCorrelation,
+				 double *indexPages);
 extern void gistcostestimate(struct PlannerInfo *root,
 				 struct IndexPath *path,
 				 double loop_count,
 				 Cost *indexStartupCost,
 				 Cost *indexTotalCost,
 				 Selectivity *indexSelectivity,
-				 double *indexCorrelation);
+				 double *indexCorrelation,
+				 double *indexPages);
 extern void spgcostestimate(struct PlannerInfo *root,
 				struct IndexPath *path,
 				double loop_count,
 				Cost *indexStartupCost,
 				Cost *indexTotalCost,
 				Selectivity *indexSelectivity,
-				double *indexCorrelation);
+				double *indexCorrelation,
+				double *indexPages);
 extern void gincostestimate(struct PlannerInfo *root,
 				struct IndexPath *path,
 				double loop_count,
 				Cost *indexStartupCost,
 				Cost *indexTotalCost,
 				Selectivity *indexSelectivity,
-				double *indexCorrelation);
+				double *indexCorrelation,
+				double *indexPages);
 
 #endif   /* INDEX_SELFUNCS_H */