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Update and extend the EXPLAIN-related documentation.

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I've made a significant effort at filling in the "Using EXPLAIN" section
to be reasonably complete about mentioning everything that EXPLAIN can
output, including the "Rows Removed" outputs that were added by Marko
Tiikkaja's recent documentation-free patch.  I also updated the examples to
be consistent with current behavior; several of them were not close to what
the current code will do.  No doubt there's more that can be done here, but
I'm out of patience for today.
This commit is contained in:
Tom Lane
2011-09-28 19:39:54 -04:00
parent cc4ff8742b
commit a32dd16459
5 changed files with 638 additions and 251 deletions
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15
doc/src/sgml/ref/analyze.sgml
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@@ -102,8 +102,9 @@ ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ ( <re
just after making major changes in the contents of a table. Accurate
statistics will help the planner to choose the most appropriate query
plan, and thereby improve the speed of query processing. A common
strategy is to run <xref linkend="sql-vacuum">
strategy for read-mostly databases is to run <xref linkend="sql-vacuum">
and <command>ANALYZE</command> once a day during a low-usage time of day.
(This will not be sufficient if there is heavy update activity.)
</para>
<para>
@@ -181,11 +182,13 @@ ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ ( <re
If the table being analyzed has one or more children,
<command>ANALYZE</command> will gather statistics twice: once on the
rows of the parent table only, and a second time on the rows of the
parent table with all of its children. The autovacuum daemon, however,
will only consider inserts or updates on the parent table when deciding
whether to trigger an automatic analyze. If that table is rarely
inserted into or updated, the inheritance statistics will not be up to date
unless you run <command>ANALYZE</command> manually.
parent table with all of its children. This second set of statistics
is needed when planning queries that traverse the entire inheritance
tree. The autovacuum daemon, however, will only consider inserts or
updates on the parent table itself when deciding whether to trigger an
automatic analyze for that table. If that table is rarely inserted into
or updated, the inheritance statistics will not be up to date unless you
run <command>ANALYZE</command> manually.
</para>
</refsect1>