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

On Sat, Oct 29, 2022 at 3:37 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2022-10-28 11:09:38 +0900, Michael Paquier wrote:
> > On Thu, Oct 27, 2022 at 03:58:25PM -0700, Andres Freund wrote:
> > > The block sizes don't need to match, do they? As long as the block is properly
> > > aligned, we can change the iov_len of the final iov to match whatever the size
> > > is being passed in, no?
> >
> > Hmm. Based on what Bharath has written upthread, it does not seem to
> > matter if the size of the aligned block changes, either:
> > https://www.postgresql.org/message-id/CALj2ACUccjR7KbKqWOsQmqH1ZGEDyJ7hH5Ef+DOhcv7+kOnjCQ@mail.gmail.com
> >
> > I am honestly not sure whether it is a good idea to make file_utils.c
> > depend on one of the compile-time page sizes in this routine, be it
> > the page size of the WAL page size, as pg_write_zeros() would be used
> > for some rather low-level operations. But we could as well just use a
> > locally-defined structure with a buffer at 4kB or 8kB and call it a
> > day?
>
> Shrug. I don't think we gain much by having yet another PGAlignedXYZBlock.

Hm. I tend to agree with Andres here, i.e. using PGAlignedBlock is
sufficient. It seems like we are using PGAlignedBlock for heap, index,
history file, fsm, visibility map file pages as well.

Please see the attached v9 patch.

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