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Reduce lock levels of CREATE TRIGGER and some ALTER TABLE, CREATE RULE actions.

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Avoid hard-coding lockmode used for many altering DDL commands, allowing easier
future changes of lock levels. Implementation of initial analysis on DDL
sub-commands, so that many lock levels are now at ShareUpdateExclusiveLock or
ShareRowExclusiveLock, allowing certain DDL not to block reads/writes.
First of number of planned changes in this area; additional docs required
when full project complete.
This commit is contained in:
Simon Riggs
2010-07-28 05:22:24 +00:00
parent 133924e13e
commit 2dbbda02e7
10 changed files with 426 additions and 232 deletions
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18
doc/src/sgml/mvcc.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.75 2010/05/03 15:35:30 alvherre Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.76 2010/07/28 05:22:24 sriggs Exp $ -->
<chapter id="mvcc">
<title>Concurrency Control</title>
@ -532,7 +532,7 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
most <productname>PostgreSQL</productname> commands automatically
acquire locks of appropriate modes to ensure that referenced
tables are not dropped or modified in incompatible ways while the
command executes. (For example, <command>ALTER TABLE</> cannot safely be
command executes. (For example, <command>TRUNCATE</> cannot safely be
executed concurrently with other operations on the same table, so it
obtains an exclusive lock on the table to enforce that.)
</para>
@ -695,8 +695,9 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
</para>
<para>
This lock mode is not automatically acquired by any
<productname>PostgreSQL</productname> command.
Acquired by <command>CREATE TRIGGER</command>,
<command>CREATE RULE</command> (except for <literal>ON SELECT</>
rules) and in some cases <command>ALTER TABLE</command>.
</para>
</listitem>
</varlistentry>
@ -742,11 +743,12 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
</para>
<para>
Acquired by the <command>ALTER TABLE</command>, <command>DROP
TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>,
Acquired by the <command>DROP TABLE</command>,
<command>TRUNCATE</command>, <command>REINDEX</command>,
<command>CLUSTER</command>, and <command>VACUUM FULL</command>
commands. This is also the default lock mode for <command>LOCK
TABLE</command> statements that do not specify a mode explicitly.
commands, as well as most variants of <command>ALTER TABLE</>.
This is also the default lock mode for <command>LOCK TABLE</command>
statements that do not specify a mode explicitly.
</para>
</listitem>
</varlistentry>