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.

1 files changed, 8 insertions, 11 deletions

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index f440875ceb1..324829690d2 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -744,10 +744,9 @@ add_path_precheck(RelOptInfo *parent_rel,
  *	  As with add_path, we pfree paths that are found to be dominated by
  *	  another partial path; this requires that there be no other references to
  *	  such paths yet.  Hence, GatherPaths must not be created for a rel until
- *	  we're done creating all partial paths for it.  We do not currently build
- *	  partial indexscan paths, so there is no need for an exception for
- *	  IndexPaths here; for safety, we instead Assert that a path to be freed
- *	  isn't an IndexPath.
+ *	  we're done creating all partial paths for it.  Unlike add_path, we don't
+ *	  take an exception for IndexPaths as partial index paths won't be
+ *	  referenced by partial BitmapHeapPaths.
  */
 void
 add_partial_path(RelOptInfo *parent_rel, Path *new_path)
@@ -826,8 +825,6 @@ add_partial_path(RelOptInfo *parent_rel, Path *new_path)
 		{
 			parent_rel->partial_pathlist =
 				list_delete_cell(parent_rel->partial_pathlist, p1, p1_prev);
-			/* we should not see IndexPaths here, so always safe to delete */
-			Assert(!IsA(old_path, IndexPath));
 			pfree(old_path);
 			/* p1_prev does not advance */
 		}
@@ -860,8 +857,6 @@ add_partial_path(RelOptInfo *parent_rel, Path *new_path)
 	}
 	else
 	{
-		/* we should not see IndexPaths here, so always safe to delete */
-		Assert(!IsA(new_path, IndexPath));
 		/* Reject and recycle the new path */
 		pfree(new_path);
 	}
@@ -1005,6 +1000,7 @@ create_samplescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer
  * 'required_outer' is the set of outer relids for a parameterized path.
  * 'loop_count' is the number of repetitions of the indexscan to factor into
  *		estimates of caching behavior.
+ * 'partial_path' is true if constructing a parallel index scan path.
  *
  * Returns the new path node.
  */
@@ -1019,7 +1015,8 @@ create_index_path(PlannerInfo *root,
 				  ScanDirection indexscandir,
 				  bool indexonly,
 				  Relids required_outer,
-				  double loop_count)
+				  double loop_count,
+				  bool partial_path)
 {
 	IndexPath  *pathnode = makeNode(IndexPath);
 	RelOptInfo *rel = index->rel;
@@ -1049,7 +1046,7 @@ create_index_path(PlannerInfo *root,
 	pathnode->indexorderbycols = indexorderbycols;
 	pathnode->indexscandir = indexscandir;
 
-	cost_index(pathnode, root, loop_count);
+	cost_index(pathnode, root, loop_count, partial_path);
 
 	return pathnode;
 }
@@ -3247,7 +3244,7 @@ reparameterize_path(PlannerInfo *root, Path *path,
 				memcpy(newpath, ipath, sizeof(IndexPath));
 				newpath->path.param_info =
 					get_baserel_parampathinfo(root, rel, required_outer);
-				cost_index(newpath, root, loop_count);
+				cost_index(newpath, root, loop_count, false);
 				return (Path *) newpath;
 			}
 		case T_BitmapHeapScan: