Re: WAL prefetch

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Cc: Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Sean Chittenden <seanc(at)joyent(dot)com>
Subject: Re: WAL prefetch
Date: 2018-06-14 12:44:58
Message-ID: CA+TgmoaNBd2KnMgone9xJXiv=0DZetJ-S9SeA=CPJJwK6kueEg@mail.gmail.com
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On Wed, Jun 13, 2018 at 11:45 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> I have tested wal_prefetch at two powerful servers with 24 cores, 3Tb NVME
>> RAID 10 storage device and 256Gb of RAM connected using InfiniBand.
>> The speed of synchronous replication between two nodes is increased from 56k
>> TPS to 60k TPS (on pgbench with scale 1000).
>
> That's a reasonable improvement.

Somehow I would have expected more. That's only a 7% speedup.

I am also surprised that HDD didn't show any improvement. Since HDD's
are bad at random I/O, I would have expected prefetching to help more
in that case.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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