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Re: VACUUM ANALYZE blocking both reads and writes to atable

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Peter Schuller <peter(dot)schuller(at)infidyne(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: VACUUM ANALYZE blocking both reads and writes to atable
Date: 2008-06-30 16:23:06
Message-ID: 20080630162306.GA18252@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-performance
Peter Schuller wrote:
> Actually, while on the topic:
> 
> >     date: 2007-09-10 13:58:50 -0400;  author: alvherre;  state: Exp;  lines: +6 -2;
> >     Remove the vacuum_delay_point call in count_nondeletable_pages, because we hold
> >     an exclusive lock on the table at this point, which we want to release as soon
> >     as possible.  This is called in the phase of lazy vacuum where we truncate the
> >     empty pages at the end of the table.
> 
> Even with the fix the lock is held. Is the operation expected to be
> "fast" (for some definition of "fast") and in-memory, or is this
> something that causes significant disk I/O and/or scales badly with
> table size or similar?

It is fast.

> I.e., is this enough that, even without the .4 bug, one should not
> really consider VACUUM ANALYZE non-blocking with respect to other
> transactions?

You should consider it non-blocking.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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