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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 (view raw or flat)
Thread:
Lists: pgsql-hackers
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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