Horton

Re: Use pg_pwritev_with_retry() instead of write() in dir_open_for_write() to avoid partial writes?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Michael Paquier <michael@paquier.xyz>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Nathan Bossart <nathandbossart@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-02-15T00:46:07Z
Lists: pgsql-hackers 
Hi,

On 2023-02-14 16:06:24 +0900, Michael Paquier wrote:
> On Mon, Feb 13, 2023 at 05:10:56PM -0800, Andres Freund wrote:
> > I just tried to use pg_pwrite_zeros - and couldn't because it doesn't have an
> > offset parameter.  Huh, what lead to the function being so constrained?
> 
> Its current set of uses cases, where we only use it now to initialize
> with zeros with WAL segments.  If you have a case that plans to use
> that stuff with an offset, no problem with me.

Then it really shouldn't have been named pg_pwrite_zeros(). The point of the
p{write,read}{,v} family of functions is to be able to specify the offset to
read/write at. I assume the p is for position, but I'm not sure.

Greetings,

Andres Freund

Commits

  1. Revise pg_pwrite_zeros()

  2. Use pg_pwrite_zeros() in walmethods.c

  3. Introduce pg_pwrite_zeros() in fileutils.c

  4. Move pg_pwritev_with_retry() to src/common/file_utils.c

  5. Restore pg_pread and friends.

  6. Remove dead pread and pwrite replacement code.