Re: Process 11812 still waiting for ExclusiveLock on extension of relation

Hi,

On Tue, Jul 17, 2012 at 7:57 PM, David Kerr <dmk(at)mr-paradox(dot)net> wrote:
> I suspect that this is related to a sustained heavy load that would stop autovacuum from
> getting at this table... Does that sound plausible?

Well, not sure. Let us look at the table's statistics first.

\x
select * from pg_stat_user_tables where relname = 'yourtablename';

> I'm wondering what options I have to smooth over these episodes / speed up the extensions.
> I'm thinking of something like, CLUSTER or VACUUM FULL (those take quite a run so I'd like
> some direction on it before i TiaS =) )

Instead of CLUSTER I would suggest you to use one of the tools below.
They do not block the table as CLUSTER does.

pg_reorg http://reorg.projects.postgresql.org/pg_reorg.html
Faster, but requires a lot of IO and additional disk space, also it
needs PK on the table.

pgcompactor http://code.google.com/p/pgtoolkit/
Allows to smooth IO, auto-determines reorganizing necessity for tables
and indexes, no PK restriction.

> I suspect that Partitioning would help. Any other ideas?

Partitioning is a good thing to think about when you deal with big tables.

>
>
> Jul 17 08:11:52 perf: [3-1] user=test,db=perf LOG: process 11812 still waiting for ExclusiveLock
> on extension of relation 60777 of database 16387 after 1000.270 ms
>
> System resouces were fine:
>
> PGDATA
> ------
> 07/17/12 08:11:48
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
> dm-2 1.20 3085.20 77.20 3994.20 15363.20 56680.00 17.69 15.57 3.82 0.06 26.22
>
> 07/17/12 08:11:53
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
> dm-2 0.40 2097.20 51.80 2610.20 10344.00 37659.20 18.03 5.23 1.96 0.05 14.28
>
>
> PGXLOG
> ------
> 07/17/12 08:11:48
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
> dm-4 0.00 3958.20 0.00 600.40 0.00 36449.60 60.71 0.44 0.74 0.73 43.54
>
> 07/17/12 08:11:53
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
> dm-4 0.00 2905.20 0.00 403.40 0.00 26492.80 65.67 0.32 0.80 0.79 31.96
>
> CPU
> ------
> CPU %user %nice %system %iowait %steal %idle
> 08:11:48 all 24.49 0.00 3.19 1.17 0.00 71.15
> 08:11:53 all 17.53 0.00 3.13 0.68 0.00 78.65
>
>
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--
Sergey Konoplev

a database architect, software developer at PostgreSQL-Consulting.com
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