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Allow DML commands that create tables to use parallel query.

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Haribabu Kommi, reviewed by Dilip Kumar and Rafia Sabih.  Various
cosmetic changes by me to explain why this appears to be safe but
allowing inserts in parallel mode in general wouldn't be.  Also, I
removed the REFRESH MATERIALIZED VIEW case from Haribabu's patch,
since I'm not convinced that case is OK, and hacked on the
documentation somewhat.

Discussion: http://postgr.es/m/CAJrrPGdo5bak6qnPWe8Kpi8g_jfQEs-G4SYmG9y+OFaw2-dPvA@mail.gmail.com
This commit is contained in:
Robert Haas
2017-10-05 11:34:38 -04:00
parent 4d85c2900b
commit e9baa5e9fa
10 changed files with 150 additions and 27 deletions
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16
doc/src/sgml/parallel.sgml
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@ -151,9 +151,10 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
<para>
The query writes any data or locks any database rows. If a query
contains a data-modifying operation either at the top level or within
a CTE, no parallel plans for that query will be generated. This is a
limitation of the current implementation which could be lifted in a
future release.
a CTE, no parallel plans for that query will be generated. As an
exception, the commands <literal>CREATE TABLE</>, <literal>SELECT
INTO</>, and <literal>CREATE MATERIALIZED VIEW</> which create a new
table and populate it can use a parallel plan.
</para>
</listitem>
@ -241,15 +242,6 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
</para>
</listitem>
<listitem>
<para>
A prepared statement is executed using a <literal>CREATE TABLE .. AS
EXECUTE ..</literal> statement. This construct converts what otherwise
would have been a read-only operation into a read-write operation,
making it ineligible for parallel query.
</para>
</listitem>
<listitem>
<para>
The transaction isolation level is serializable. This situation