Re: increasing the default WAL segment size

From: Beena Emerson <memissemerson(at)gmail(dot)com>
To: Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
Cc: Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: increasing the default WAL segment size
Date: 2017-03-10 05:53:57
Message-ID: CAOG9ApEhqTX66=UeAQJjQG3jPnnFZiz9voVVWVZwyOA=drzjgQ@mail.gmail.com
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Hello,

On Tue, Mar 7, 2017 at 10:46 AM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
wrote:

> Hi,
>
> I took a look at this patch. Overall, the patch looks good to me.
> However, there are some review comments that I would like to share,
>
> 1. I think the macro 'PATH_MAX' used in pg_waldump.c file is specific
> to Linux. It needs to be changed to some constant value or may be
> MAXPGPATH inorder to make it platform independent.
>
> 2. As already mentioned by Jim and Kuntal upthread, you are trying to
> detect the configured WAL segment size in pg_waldump.c and
> pg_standby.c files based on the size of the random WAL file which
> doesn't look like a good idea. But, then I think the only option we
> have is to pass the location of pg_control file to pg_waldump module
> along with the start and end wal segments.
>
> 3. When trying to compile '02-initdb-walsegsize-v2.patch' on Windows,
> I got this warning message,
>
> Warning 1 warning C4005: 'DEFAULT_XLOG_SEG_SIZE' : macro
> redefinition
> c:\users\ashu\postgresql\src\include\pg_config_manual.h 20
>
> Apart from these, I am not having any comments as of now. I am still
> validating the patch on Windows. If I find any issues i will update
> it.
>
> Thank you for your reviews Kuntal, Jim, Ashutosh

Attached in an updated 02 patch which:

1. Call RetrieveXLogSegSize(conn) in pg_receivewal.c
2. Remove the warning in Windows
3. Change PATH_MAX in pg_waldump with MAXPGPATH

Regarding the usage of the wal file size as the XLogSegSize, I agree with
what Robert has said. Generally, the wal size will be of the expected
wal_segment_size and to have it any other size, esspecially of a valid
power2 value is extremely rare and I feel it is not a major cause of
concern.

Thank you,

Beena Emerson
EnterpriseDB: http://www.enterprisedb.com

Attachment Content-Type Size
01-add-XLogSegmentOffset-macro.patch application/octet-stream 16.5 KB
02-initdb-walsegsize-v3.patch application/octet-stream 34.0 KB

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