Message-ID: <8f67073e5a6818a17eef5c44b087640db8939f7d.camel@cybertec.at>
Subject: Re: pg_attribute, pg_class, pg_depend grow huge in count and size
 with multiple tenants.
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Avinash Kumar <avinash.vallarapu@gmail.com>
Cc: Rory Campbell-Lange <rory@campbell-lange.net>, "David G. Johnston"
	 <david.g.johnston@gmail.com>, samhitha g <samhithagarudadri@gmail.com>,
	pgsql-performance@lists.postgresql.org
Date: Fri, 08 May 2020 08:53:41 +0200
In-Reply-To: 
 <CAN0TujdKpqFQPVLtWDNagv3Y-LgyrMrzCKpr3fib7sKgq_w5uQ@mail.gmail.com>
References: 
	<CAG5FJBVFp4TtEde-xn2hpYQKByFxPQChXitrLorwyiN71+cPyA@mail.gmail.com>
	 <CAKFQuwafqFBr+jJ9fGie19CCDoBiGarJejhcwiYHaYyM+kY_kQ@mail.gmail.com>
	 <CAN0TujdCgR5TA4JW6T5Di6nL5RVShbUAfY+G-7Fc-ABH4U=--g@mail.gmail.com>
	 <20200507210846.GA17040@campbell-lange.net>
	 <CAN0TujfLZ22xm0u99B+jsB31R55fQ5OJ2PKgcmr0TZHUPwoTUw@mail.gmail.com>
	 <17c5b15451fac2ace7a815d1d2c8f86e1d232802.camel@cybertec.at>
	 <CAN0TujdKpqFQPVLtWDNagv3Y-LgyrMrzCKpr3fib7sKgq_w5uQ@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.32.5 (3.32.5-1.fc30) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Fri, 2020-05-08 at 03:47 -0300, Avinash Kumar wrote:
> > Just set "autovacuum_max_workers" higher.
> 
> No, that wouldn't help. If you just increase autovacuum_max_workers, the total cost limit of
> autovacuum_vacuum_cost_limit (or vacuum_cost_limit) is shared by so many workers and it
> further delays autovacuum per each worker. Instead you need to increase autovacuum_vacuum_cost_limit
> as well when you increase the number of workers.

True, I should have mentioned that.

> But, if you do that and also increase workers, well, you would easily reach the limitations
> of the disk. I am not sure it is anywhere advised to have 20 autovacuum_max_workers unless
> i have a disk with lots of IOPS and with very tiny tables across all the databases.

Sure, if you have a high database load, you will at some point exceed the limits of
the machine, which is not surprising.  What I am trying to say is that you have to ramp
up the resources for autovacuum together with increasing the overall workload.
You should consider autovacuum as part of that workload.

If your machine cannot cope with the workload any more, you have to scale, which
is easily done by adding more machines if you have many databases.

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