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Clarify runtime pruning in EXPLAIN

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Author: Amit Langote
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/002dec69-9afb-b621-5630-235eceafe0bd@lab.ntt.co.jp
This commit is contained in:
Alvaro Herrera 2018-12-17 11:44:36 -03:00
parent 3abb11e55b
commit 1e6240a3fe
1 changed files with 6 additions and 2 deletions
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doc/src/sgml/ddl.sgml
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@ -4421,8 +4421,12 @@ EXPLAIN SELECT count(*) FROM measurement WHERE logdate >= DATE '2008-01-01';
query, partition pruning is performed whenever one of the
execution parameters being used by partition pruning changes.
Determining if partitions were pruned during this phase requires
careful inspection of the <literal>nloops</literal> property in
the <command>EXPLAIN ANALYZE</command> output.
careful inspection of the <literal>loops</literal> property in
the <command>EXPLAIN ANALYZE</command> output. Subplans
corresponding to different partitions may have different values
for it depending on how many times each of them was pruned during
execution. Some may be shown as <literal>(never executed)</literal>
if they were pruned every time.
</para>
</listitem>
</itemizedlist>