Re: Remove the comment on the countereffectiveness of large shared_buffers on Windows

From: "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>
To: 'Amit Kapila' <amit(dot)kapila16(at)gmail(dot)com>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Remove the comment on the countereffectiveness of large shared_buffers on Windows
Date: 2016-11-17 05:30:14
Message-ID: 0A3221C70F24FB45833433255569204D1F6415A0@G01JPEXMBYT05
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From: pgsql-hackers-owner(at)postgresql(dot)org
> [mailto:pgsql-hackers-owner(at)postgresql(dot)org] On Behalf Of Amit Kapila
> > I think the reason why increasing shared_buffers didn't give better
> performance for read-only tests than you expect is that the relation files
> are cached in the filesystem cache. The purpose of this verification is
> to know that the effective upper limit is not 512MB (which is too small
> now), and I think the purpose is achieved. There may be another threshold,
> say 32GB or 128GB, over which the performance degrades due to PostgreSQL
> implementation, but that's another topic which also applies to other OSes.
> >
> If we don't get any benefit by increasing the shared_buffers on windows,
> then what advantage do you see in recommending higher value?

No, I'm not recommending a higher value, but just removing the doubtful sentences of 512MB upper limit. The advantage is that eliminating this sentence will make a chance for users to try best setting.

> I generally run it for 20 to 30 mins for read-write tests. Also, to ensure
> consistent data, please consider changing following parameters in
> postgresql.conf checkpoint_timeout = 35 minutes or so, min_wal_size = 5GB
> or so, max_wal_size = 20GB or so and checkpoint_completion_target=0.9.
> Apart from above, ensure to run manual checkpoint (checkpoint command) after
> each test.

Thank you, I'll try the read-write test with these settings on the weekend, when my PC is available. I understood that your intention is to avoid being affected by checkpointing and WAL segment creation.

Takayuki Tsunakawa

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