vacuum is time consuming

Assuming that the system is online and in use, you may want to consider
doing analyze first to ensure stats are proper, and then vacuum all
less-used tables that should be quick then larger/more active tables with
the verbose option to see details of why it might be taking time. If you
are seeing multiple index scan steps, then maintenance_work_mem is lower
than ideal. If you are using default vacuum settings, there is no I/O
throttling as I understand the vacuum_cost_delay and vacuum_cost_limit
settings. What is your concern with it taking time? Depending how you did
the upgrade, there may be no (new/special) need to do the vacuum at all
also.

Hi Atul,

We have DB of 400GBs, Server RAM is 160GBs. CPU consumption is 1-3% only.

We have configured maintenance_work_mem to 10GBs and restarted the
postgres service.

Just wanted to mention that maintenance_work_mem has a hardcoded upper
limit threshold of 1GB, so any size bigger than that to
maintenance_work_mem or autovacuum_maintenance_work_mem will leave it
effectively at 1GB.

There have been a few attempts the past few years on lifting that restriction.

We have done upgrade from postgres 9.5 to 9.6, then when we run vacuum
analyze on database, it is taking more than 5 hours and still running.

Any suggestions for making the process(vacuum analyze) faster are welcome.

Yes, upgrade to PG13.

Kind regards, Martin,

--
Martín Marqués
It’s not that I have something to hide,
it’s that I have nothing I want you to see

Ok Martin, I got ur ur point of max limit of maintenance_work_mem is 1 GB
but there is nothing mentioned about the same in postgresql.conf as remarks
for this specific parameter.

Is there any other option to increase the speed of vacuum?

Regards
Atul

On Tuesday, February 2, 2021, Martín Marqués <martin.marques@gmail.com>
wrote:

On Tue, 2021-02-02 at 13:44 +0530, Atul Kumar wrote:

Is there any other option to increase the speed of vacuum?

For autovacuum, decrease "autovacuum_vacuum_cost_delay".

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

Hi,

Is there any other option to increase the speed of vacuum?

For autovacuum, decrease "autovacuum_vacuum_cost_delay".

He mentioned in the original message that his problems was with a
global VACUUM after upgrading, so cost_delay should be zero by
default.

Regards,

--
Martín Marqués
It’s not that I have something to hide,
it’s that I have nothing I want you to see