Re: autovacuum disk IO

Le 2 mars 2016 16:25:10 GMT+01:00, Artem Tomyuk <admin@leboutique.com> a écrit :
>Hi.
>
>I've noticed that autovac. process worked more than 10 minutes, during
>this
>zabbix logged more than 90% IO disk utilization on db volume....
>
>===========>29237   2016-03-02 15:17:23 EET 00000 [24-1]LOG:
>automatic vacuum of table "lb_upr.public._reference32": index scans: 1
>    pages: 0 removed, 263307 remain
>    tuples: 298 removed, 1944753 remain, 0 are dead but not yet removable
>    buffer usage: 67814 hits, 265465 misses, 15647 dirtied
>    avg read rate: 3.183 MB/s, avg write rate: 0.188 MB/s

According to what I am reading here, your autovacumm avg read activity was less than 4MB/s...and 188kB/s for writes.

I seriously doubt these numbers are high enough to saturate your disks bandwidth.

>    *system usage: CPU 5.34s/6.27u sec elapsed 651.57 sec*

This tells that the autovacumm tooks 651s to complete...but only 5s and 6s of cpu in kernel and userland in total.

Autovacuum are slowed down thanks to autovacumm_vacuum_cost_delay param, which explains the 10min run and such a low
diskactivity. 

>Is it possible to log autovac. io impact during it execution?

I would bet the problem is elsewhere...

/Ioguix