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Re: BUG #5946: Long exclusive lock taken by vacuum (not full)

From: Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #5946: Long exclusive lock taken by vacuum (not full)
Date: 2011-03-25 21:43:03
Message-ID: AANLkTi=RtuZSVLUwWWfrEbYkA19thJ82Ub67ODTRPkux@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On Sat, Mar 26, 2011 at 4:17 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "Maxim Boguk" <Maxim(dot)Boguk(at)gmail(dot)com> writes:
> > In my case vacuum tried to truncate last 10-15GB from 100Gb relation, and
> > each time (3) it was cost 10+ minutes of service downtime (because that
> > table was completely locked).
>
> > Is  that correct behaviour? Are here any way to speedup that process or
> at
> > least allow read-only queries during that time?
>
> Use autovacuum --- if there's something that wants to access the table,
> autovac will get kicked off the lock.  (Of course, the table may never
> get truncated then, but maybe you don't care.)
>
>                        regards, tom lane
>

Thank you for an idea.

Are having lots empty pages at end of the table can have any negative impact
on database performance (assuming I have plenty of free disk space)?
In my case these 100Gb table going to be reduced to 20Gb size actual data
located at start of the table, so I worry about possible negative impact of
having extra 80Gb free space at end of the table.

Regards,
Maxim

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Subject: Re: BUG #5946: Long exclusive lock taken by vacuum (not full)
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