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

On Sat, Sep 24, 2022 at 1:54 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> +        PGAlignedXLogBlock zbuffer;
> +
> +        memset(zbuffer.data, 0, XLOG_BLCKSZ);
>
> This seems excessive for only writing a single byte.

Yes, I removed it now, instead doing pg_pwrite(fd, "\0", 1,
wal_segment_size - 1).

> +#ifdef WIN32
> +        /*
> +         * XXX: It looks like on Windows, we need an explicit lseek() call here
> +         * despite using pwrite() implementation from win32pwrite.c. Otherwise
> +         * an error occurs.
> +         */
>
> I think this comment is too vague.  Can we describe the error in more
> detail?  Or better yet, can we fix it as a prerequisite to this patch set?

The commit b6d8a60aba322678585ebe11dab072a37ac32905 brings back
pg_pwrite() and its friends. This puts the responsibility of doing
lseek(SEEK_SET) on the callers if they wish to.

Please see the v5 patch set and review it further.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com