Horton

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

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-06T06:41:18Z
Lists: pgsql-hackers 
On Fri, Aug 05, 2022 at 03:55:26PM +0530, Bharath Rupireddy wrote:
> I noticed that dir_open_for_write() in walmethods.c uses write() for
> WAL file initialization (note that this code is used by pg_receivewal
> and pg_basebackup) as opposed to core using pg_pwritev_with_retry() in
> XLogFileInitInternal() to avoid partial writes. Do we need to fix
> this?

0d56acfb has moved pg_pwritev_with_retry to be backend-only in fd.c :/

> Thoughts?

Makes sense to me for the WAL segment pre-padding initialization, as
we still want to point to the beginning of the segment after we are
done with the pre-padding, and the code has an extra lseek().
--
Michael

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.