From e6858e665731c0f56d3ecc9fbb245c32d24f8ef7 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 14 Oct 2011 17:23:01 -0400 Subject: Measure the number of all-visible pages for use in index-only scan costing. Add a column pg_class.relallvisible to remember the number of pages that were all-visible according to the visibility map as of the last VACUUM (or ANALYZE, or some other operations that update pg_class.relpages). Use relallvisible/relpages, instead of an arbitrary constant, to estimate how many heap page fetches can be avoided during an index-only scan. This is pretty primitive and will no doubt see refinements once we've acquired more field experience with the index-only scan mechanism, but it's way better than using a constant. Note: I had to adjust an underspecified query in the window.sql regression test, because it was changing answers when the plan changed to use an index-only scan. Some of the adjacent tests perhaps should be adjusted as well, but I didn't do that here. --- doc/src/sgml/catalogs.sgml | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'doc/src') diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index 0495bd03bd5..e830c5f3d44 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -1654,6 +1654,19 @@ + + relallvisible + int4 + + + Number of pages that are marked all-visible in the table's + visibility map. This is only an estimate used by the + planner. It is updated by VACUUM, + ANALYZE, and a few DDL commands such as + CREATE INDEX. + + + reltoastrelid oid -- cgit v1.2.3