From: Grigory Smolkin <g.smolkin@postgrespro.ru>
To: pgsql-hackers@lists.postgresql.org
Subject: Re: [PATCH] xlogreader: do not read a file block twice
Date: Mon, 11 Feb 2019 19:32:59 +0300
Message-ID: <87e30af6-f85a-dc95-4574-95cded028786@postgrespro.ru> (raw)
In-Reply-To: <2ddf4a32-517e-d6f4-d992-4a63b6035bfd@postgrespro.ru>
References: <2ddf4a32-517e-d6f4-d992-4a63b6035bfd@postgrespro.ru>
Hm, looks like it could speed up PostgreSQL recovery, but is it safe?
On 02/11/2019 07:25 PM, Arthur Zakirov wrote:
> Hello hackers,
>
> Grigory noticed that one of our utilities has very slow performance
> when xlogreader reads zlib archives. We found out that xlogreader
> sometimes reads a WAL file block twice.
>
> zlib has slow performance when you read an archive not in sequential
> order. I think reading a block twice in same position isn't
> sequential, because gzread() moves current position forward and next
> call gzseek() to the same position moves it back.
>
> It seems that the attached patch solves the issue. I think when reqLen
> == state->readLen the requested block already is in the xlogreader's
> buffer.
>
> What do you think?
>
--
Grigory Smolkin
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
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To: pgsql-hackers@postgresql.org
Cc: g.smolkin@postgrespro.ru, pgsql-hackers@lists.postgresql.org
Subject: Re: [PATCH] xlogreader: do not read a file block twice
In-Reply-To: <87e30af6-f85a-dc95-4574-95cded028786@postgrespro.ru>
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