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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2011-10-14 17:23:01 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2011-10-14 17:23:46 -0400 |
| commit | e6858e665731c0f56d3ecc9fbb245c32d24f8ef7 (patch) | |
| tree | 4df2705d53d53b1bbd7a14d7017cb519d82ee227 /doc/src | |
| parent | dea95c7a7beb5ef66ce89269dd0e84d0c26e5523 (diff) | |
| download | postgresql-e6858e665731c0f56d3ecc9fbb245c32d24f8ef7.tar.gz postgresql-e6858e665731c0f56d3ecc9fbb245c32d24f8ef7.zip | |
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.
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/catalogs.sgml | 13 |
1 files changed, 13 insertions, 0 deletions
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 @@ -1655,6 +1655,19 @@ </row> <row> + <entry><structfield>relallvisible</structfield></entry> + <entry><type>int4</type></entry> + <entry></entry> + <entry> + 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 <command>VACUUM</command>, + <command>ANALYZE</command>, and a few DDL commands such as + <command>CREATE INDEX</command>. + </entry> + </row> + + <row> <entry><structfield>reltoastrelid</structfield></entry> <entry><type>oid</type></entry> <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry> |