Re: Lock levels for ALTER TABLE

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Lock levels for ALTER TABLE
Date: 2013-01-10 04:02:54
Message-ID: 20130110040254.GA24282@momjian.us
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On Wed, Jan 9, 2013 at 10:27:54PM -0500, Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > EnterpriseDB reports that our documentation states that ALTER TABLE
> > takes SHARE UPDATE EXCLUSIVE and ACCESS EXCLUSIVE lock modes.
>
> Where do they see that? We certainly reverted all of the documentation
> that Simon changed in the original commit for that failed feature.
> Something might have slipped through the cracks though.

In mvcc.sgml, I see:

<varlistentry>
<term>
<literal>SHARE UPDATE EXCLUSIVE</literal>
</term>
<listitem>
<para>
Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>,
<literal>SHARE</literal>, <literal>SHARE ROW
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes.
This mode protects a table against
concurrent schema changes and <command>VACUUM</> runs.
</para>

<para>
Acquired by <command>VACUUM</command> (without <option>FULL</option>),
<command>ANALYZE</>, <command>CREATE INDEX CONCURRENTLY</>, and
--> some forms of <command>ALTER TABLE</command>.
</para>
</listitem>
</varlistentry>

and

<varlistentry>
<term>
<literal>ACCESS EXCLUSIVE</literal>
</term>
<listitem>
<para>
Conflicts with locks of all modes (<literal>ACCESS
SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW
EXCLUSIVE</literal>, <literal>SHARE UPDATE
EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE
ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal>).
This mode guarantees that the
holder is the only transaction accessing the table in any way.
</para>

<para>
--> Acquired by the <command>ALTER TABLE</>, <command>DROP TABLE</>,
<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.
</para>
</listitem>
</varlistentry>

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +

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