public inbox for [email protected]  

help / color / mirror / Atom feed

From: Magnus Hagander <[email protected]>
To: Julien Rouhaud <[email protected]>
Cc: Don Seiler <[email protected]>
Cc: pgsql-admin <[email protected]>
Subject: Re: Estimating HugePages Requirements?
Date: Wed, 9 Jun 2021 21:07:09 +0200
Message-ID: <CABUevExXvoPvLN70CznmQfbjwxnrdXo9gXxZwGpBoUhjtFi3Ng@mail.gmail.com> (raw)
In-Reply-To: <CAOBaU_ZHtRhG+MvoT6=HpbMoK=JnsJHBMmxQ-XLSVoh6fFqJHQ@mail.gmail.com>
References: <CAHJZqBBLHFNs6it-fcJ6LEUXeC5t73soR3h50zUSFpg7894qfQ@mail.gmail.com>
	<CAOBaU_ZHtRhG+MvoT6=HpbMoK=JnsJHBMmxQ-XLSVoh6fFqJHQ@mail.gmail.com>

On Wed, Jun 9, 2021 at 7:23 PM Julien Rouhaud <[email protected]> wrote:
>
> On Thu, Jun 10, 2021 at 12:42 AM Don Seiler <[email protected]> wrote:
> >
> > I'm told other factors contribute to this additional memory requirement, such as max_connections, wal_buffers, etc. I'm wondering if anyone has been able to come up with a reliable method for determining the HugePages requirements for a PG cluster based on the GUC values (that would be known at deployment time).
>
> It also depends on modules like pg_stat_statements and their own
> configuration.  I think that you can find the required size that your
> current configuration will allocate with:
>
> SELECT sum(allocated_size) FROM pg_shmem_allocations ;

I wonder how hard it would be to for example expose that through a
commandline switch or tool.

The point being that in order to run the query you suggest, the server
must already be running. There is no way to use this to estimate the
size that you're going to need after changing the value of
shared_buffers, which is a very common scenario. (You can change it,
restart without using huge pages because it fails, run that query,
change huge pages, and restart again -- but that's not exactly...
convenient)

-- 
 Magnus Hagander
 Me: https://www.hagander.net/
 Work: https://www.redpill-linpro.com/

view thread (108+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: Estimating HugePages Requirements?
  In-Reply-To: <CABUevExXvoPvLN70CznmQfbjwxnrdXo9gXxZwGpBoUhjtFi3Ng@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox