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, 14 insertions, 13 deletions

diff --git a/src/test/regress/expected/rangefuncs.out b/src/test/regress/expected/rangefuncs.out
index 51d561b28f..5f20c93249 100644
--- a/src/test/regress/expected/rangefuncs.out
+++ b/src/test/regress/expected/rangefuncs.out
@@ -1,17 +1,18 @@
 SELECT name, setting FROM pg_settings WHERE name LIKE 'enable%';
-       name        | setting 
--------------------+---------
- enable_bitmapscan | on
- enable_hashagg    | on
- enable_hashjoin   | on
- enable_indexscan  | on
- enable_material   | on
- enable_mergejoin  | on
- enable_nestloop   | on
- enable_seqscan    | on
- enable_sort       | on
- enable_tidscan    | on
-(10 rows)
+         name         | setting 
+----------------------+---------
+ enable_bitmapscan    | on
+ enable_hashagg       | on
+ enable_hashjoin      | on
+ enable_indexonlyscan | on
+ enable_indexscan     | on
+ enable_material      | on
+ enable_mergejoin     | on
+ enable_nestloop      | on
+ enable_seqscan       | on
+ enable_sort          | on
+ enable_tidscan       | on
+(11 rows)
 
 CREATE TABLE foo2(fooid int, f2 int);
 INSERT INTO foo2 VALUES(1, 11);