Support index-only scans using the visibility map to avoid heap fetches.

When a btree index contains all columns required by the query, and the
visibility map shows that all tuples on a target heap page are
visible-to-all, we don't need to fetch that heap page.  This patch depends
on the previous patches that made the visibility map reliable.

There's a fair amount left to do here, notably trying to figure out a less
chintzy way of estimating the cost of an index-only scan, but the core
functionality seems ready to commit.

Robert Haas and Ibrar Ahmed, with some previous work by Heikki Linnakangas.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 8a3a5d85e2a..742e7a880ad 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -210,6 +210,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			info->relam = indexRelation->rd_rel->relam;
 			info->amcostestimate = indexRelation->rd_am->amcostestimate;
 			info->amcanorderbyop = indexRelation->rd_am->amcanorderbyop;
+			info->amcanreturn = indexRelation->rd_am->amcanreturn;
 			info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
 			info->amsearchnulls = indexRelation->rd_am->amsearchnulls;
 			info->amhasgettuple = OidIsValid(indexRelation->rd_am->amgettuple);