Add optimizer and executor support for parallel index scans.

In combination with 569174f, 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.

Author: robertmhaas

contrib/bloom/blcost.c

@@ -24,7 +24,8 @@
 void
 blcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 			   Cost *indexStartupCost, Cost *indexTotalCost,
-			   Selectivity *indexSelectivity, double *indexCorrelation)
+			   Selectivity *indexSelectivity, double *indexCorrelation,
+			   double *indexPages)
 {
 	IndexOptInfo *index = path->indexinfo;
 	List	   *qinfos;
@@ -45,4 +46,5 @@ blcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 	*indexTotalCost = costs.indexTotalCost;
 	*indexSelectivity = costs.indexSelectivity;
 	*indexCorrelation = costs.indexCorrelation;
+	*indexPages = costs.numIndexPages;
 }

contrib/bloom/bloom.h

@@ -208,6 +208,6 @@ extern bytea *bloptions(Datum reloptions, bool validate);
 extern void blcostestimate(PlannerInfo *root, IndexPath *path,
 			   double loop_count, Cost *indexStartupCost,
 			   Cost *indexTotalCost, Selectivity *indexSelectivity,
-			   double *indexCorrelation);
+			   double *indexCorrelation, double *indexPages);
 
 #endif

contrib/bloom/blutils.c

@@ -119,6 +119,7 @@ blhandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = false;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = blbuild;

doc/src/sgml/indexam.sgml

@@ -110,6 +110,8 @@ 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;
 

src/backend/access/brin/brin.c

@@ -93,6 +93,7 @@ brinhandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = true;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = brinbuild;

src/backend/access/gin/ginutil.c

@@ -50,6 +50,7 @@ ginhandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = true;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = ginbuild;

src/backend/access/gist/gist.c

@@ -71,6 +71,7 @@ gisthandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = true;
 	amroutine->amclusterable = true;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = gistbuild;

src/backend/access/hash/hash.c

@@ -67,6 +67,7 @@ hashhandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = false;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = INT4OID;
 
 	amroutine->ambuild = hashbuild;

src/backend/access/nbtree/nbtree.c

@@ -140,6 +140,7 @@ bthandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = false;
 	amroutine->amclusterable = true;
 	amroutine->ampredlocks = true;
+	amroutine->amcanparallel = true;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = btbuild;

src/backend/access/spgist/spgutils.c

@@ -49,6 +49,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = false;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
+	amroutine->amcanparallel = false;
 	amroutine->amkeytype = InvalidOid;
 
 	amroutine->ambuild = spgbuild;