Date: Tue, 11 Sep 2012 15:59:40 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
To: AI Rumman <rummandba@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: add column with default value is very slow
Message-ID: <20120911135939.GA1656@depesz.com>
Reply-To: depesz@depesz.com
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On Tue, Sep 11, 2012 at 07:55:24PM +0600, AI Rumman wrote:
> I added the excel file for locks data.

well, it worked, but why didn't you just make it text file, in notepad or
something like this?

> I was surprised to see that while I was updating a single column value for
> all records in a tables, all indexes are locked by the server.

alter table is not locked (At least looking at the pg_locks data you
showed).

this means - it just takes long time.

Please do:
select pg_total_relation_size('entity');
to see how much data it has to rewrite.

for future - just don't do alter table, with default, and not null.
doing it via add column; set default; batch-backfill data, set not null
will take longer but will be done with much shorter locks.

Best regards,

depesz

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