Horton

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

Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

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From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-07T01:12:11Z
Lists: pgsql-hackers

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On Sat, Aug 6, 2022 at 12:11 PM Michael Paquier <michael@paquier.xyz> wrote:
>
> 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 :/

Yeah. pg_pwritev_with_retry can also be part of common/file_utils.c/.h
so that everyone can use it.

> > 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().

Thanks. I attached the v1 patch, please review it.

-- 
Bharath Rupireddy
RDS Open Source Databases: https://aws.amazon.com/rds/postgresql/

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.