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

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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.
This commit is contained in:
Tom Lane
2011-10-07 20:13:02 -04:00
parent caa1054df8
commit a2822fb933
34 changed files with 704 additions and 203 deletions
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7
doc/src/sgml/ref/postgres-ref.sgml
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@ -376,12 +376,15 @@ PostgreSQL documentation
<variablelist>
<varlistentry>
<term><option>-f</option> <literal>{ s | i | m | n | h }</literal></term>
<term><option>-f</option> <literal>{ s | i | o | b | t | n | m | h }</literal></term>
<listitem>
<para>
Forbids the use of particular scan and join methods:
<literal>s</literal> and <literal>i</literal>
disable sequential and index scans respectively, while
disable sequential and index scans respectively,
<literal>o</literal>, <literal>b</literal> and <literal>t</literal>
disable index-only scans, bitmap index scans, and TID scans
respectively, while
<literal>n</literal>, <literal>m</literal>, and <literal>h</literal>
disable nested-loop, merge and hash joins respectively.
</para>