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Re: Unusually high IO for autovacuum worker

From: Vlad Bailescu <vlad(at)mojitosoftware(dot)com>
To: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Unusually high IO for autovacuum worker
Date: 2013-02-01 09:54:39
Message-ID: CABrmO8qoc7sJYdNZKF2dERPqeAxu8EgG-iU-R7Jfj3AieF-L5g@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
On Fri, Feb 1, 2013 at 11:01 AM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>wrote:

>
> Do you know for sure that its the master table that generating all the
> vacuum traffic ? What about the partition tables ? Do they get any
> updates/deletes ? It might be useful if you could turn autovacuum
> logging ON and see which tables are getting vacuumed and correlate
> that with the increased IO activity that you're seeing.
>
> Did you change any other parameters like checkpoint timeout/segments
> etc ? It might be worthwhile to log checkpoint activities as well to
> be doubly sure.
>
> Thanks,
> Pavan
>

 I'm pretty sure the io is from the autovacuum on master table because it's
last_autovacuum stats update almost every minute and iotop shows something
like:

Total DISK READ:       5.80 M/s | Total DISK WRITE:     115.85 K/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>
COMMAND


 7681 be/4 postgres    5.93 M/s    0.00 B/s  0.00 % 63.62 % postgres:
autovacuum worker process   fleet
15837 be/4 postgres    0.00 B/s   23.17 K/s  0.00 %  4.98 % postgres: fleet
fleet 127.0.0.1(53537) idle
16683 be/4 postgres    0.00 B/s   23.17 K/s  0.00 %  2.68 % postgres: fleet
fleet 127.0.0.1(53978) idle
18599 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  1.25 % postgres: fleet
fleet 127.0.0.1(59529) idle
15608 be/4 postgres    0.00 B/s   23.17 K/s  0.00 %  0.04 % postgres: fleet
fleet 127.0.0.1(53349) idle
10253 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: fleet
fleet 127.0.0.1(50639) idle
16524 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: fleet
fleet 127.0.0.1(53939) idle
10248 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: fleet
fleet 127.0.0.1(50634) idle
18606 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: fleet
fleet 127.0.0.1(59535) idle
14849 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: fleet
fleet 127.0.0.1(52832) idle
30308 be/4 postgres    0.00 B/s    7.72 K/s  0.00 %  0.01 % postgres: wal
writer process
21528 be/4 www-data    0.00 B/s    3.86 K/s  0.00 %  0.00 % nginx: worker
process
30307 be/4 postgres    0.00 B/s   38.62 K/s  0.00 %  0.00 % postgres:
writer process

I just checked and our config only sets:

max_connections = 210
superuser_reserved_connections = 10

wal_buffers = 8MB

checkpoint_segments = 16
checkpoint_completion_target = 0.9

random_page_cost = 3.0

shared_buffers = 9GB
effective_cache_size = 28GB
work_mem = 88MB
maintenance_work_mem = 1GB

We're running on a server with 40GB RAM and a RAID 10 over 6 10k HDDs.

Stats show only 3 tables get frequently autovacuumed

     Table Name Tuples inserted Tuples updated Tuples deleted Tuples HOT
updated Live Tuples Dead Tuples Last vacuum Last autovacuum Last analyze Last
autoanalyze Vacuum counter Autovacuum counter Analyze counter Autoanalyze
counter Size  vehicle_position 4689127 0 4689127 0 0 1985
2013-02-01 11:46:46.441227+02 2013-01-31 14:48:00.775864+02 2013-02-01
11:46:46.494234+02 0 3761 1 3754 4016 kB  vehicle 2124 934640 0 924003 2124
390
2013-02-01 11:47:46.067695+02 2013-02-01 11:47:46.325444+02 0 1293 0 2038 2448
kB  input_current 10032 1649206 0 1635902 10032 1728
2013-02-01 11:45:46.0681+02 2013-02-01 11:45:46.215048+02 0 442 0 1294 2336
kB

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