Horton

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

Nathan Bossart <nathandbossart@gmail.com>

View thread View on postgr.es
From: Nathan Bossart <nathandbossart@gmail.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Michael Paquier <michael@paquier.xyz>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-26T21:55:31Z
Lists: pgsql-hackers 
On Tue, Sep 27, 2022 at 10:37:38AM +1300, Thomas Munro wrote:
> I don't think so, that's an extra kernel call.  I think I'll just have
> to revert part of my recent change that removed the pg_ prefix from
> those function names in our code, and restore the comment that warns
> you about the portability hazard (I thought it went away with HP-UX
> 10, where we were literally calling lseek() before every write()).
> The majority of users of these functions don't intermix them with
> calls to read()/write(), so they don't care about the file position,
> so I think it's just something we'll have to continue to be mindful of
> in the places that do.

Ah, you're right, it's probably best to avoid the extra system call for the
majority of callers that don't care about the file position.  I retract my
previous message.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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.