From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
---|---|
To: | Steve Crawford <scrawford(at)pinpointresearch(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Vacuum-full very slow |
Date: | 2007-04-25 19:04:20 |
Message-ID: | 20070425190420.GK7969@alvh.no-ip.org |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general pgsql-hackers |
Steve Crawford wrote:
> So my mental-model is utterly and completely wrong. My assumption was
> that since a full vacuum requires an access exclusive lock, it would do
> the intelligent and efficient thing which would be to first compact the
> table and then recreate the indexes.
Right, it doesn't do the intelligent and efficient thing. There are
differences though: VACUUM FULL does not need an extra copy of the table
and indexes, while CLUSTER does.
OTOH, VACUUM FULL also needs to WAL log every action, which makes it
slower; CLUSTER only calls fsync when it's done, but since it keeps the
original files around it doesn't need to involve WAL.
> Am I reading that what it actually does is to thrash around keeping
> indexes unnecessarily updated, bloating them in the process?
Yes.
> Will cluster reduce the on-disk size like vacuum does?
Yes. And a bit more because indexes don't suffer.
> And am I the only one who thinks the cluster command is backwards -
> after all it is the table that is being reordered based on an index so:
No, you're not, which is why a new syntax has been introduced for 8.3.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
From | Date | Subject | |
---|---|---|---|
Next Message | Richard Broersma Jr | 2007-04-25 19:07:29 | Re: PosegreSQL support |
Previous Message | Richard Huxton | 2007-04-25 19:01:38 | Re: PosegreSQL support |
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2007-04-25 19:07:21 | Re: BUG #3245: PANIC: failed to re-find shared loc k o b j ect |
Previous Message | Mark Wong | 2007-04-25 18:54:38 | Re: ECPG failure on BF member Vaquita (Windows Vista) |