Horton

Re: Direct I/O

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>, Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>, Christoph Berg <myon@debian.org>, mikael.kjellstrom@gmail.com, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-04-30T04:11:06Z
Lists: pgsql-hackers 
On Mon, Apr 17, 2023 at 12:06:23PM -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Sat, Apr 15, 2023 at 2:19 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> I get the impression that we are going to need an actual runtime
> >> test if we want to defend against this.  Not entirely convinced
> >> it's worth the trouble.  Who, other than our deliberately rear-guard
> >> buildfarm animals, is going to be building modern PG with such old
> >> compilers?  (And more especially to the point, on platforms new
> >> enough to have working O_DIRECT?)
> 
> > I don't think that I fully understand everything under discussion
> > here, but I would just like to throw in a vote for trying to make
> > failures as comprehensible as we reasonably can.
> 
> I'm not hugely concerned about this yet.  I think the reason for
> slipping this into v16 as developer-only code is exactly that we need
> to get a feeling for where the portability dragons live.

Speaking of the developer-only status, I find the io_direct name more enticing
than force_parallel_mode, which PostgreSQL renamed due to overuse from people
expecting non-developer benefits.  Should this have a name starting with
debug_?

Commits

  1. Rename hook functions for debug_io_direct to match variable name.

  2. Rename io_direct to debug_io_direct.

  3. Skip the 004_io_direct.pl test if a pre-flight check fails.

  4. Use higher wal_level for 004_io_direct.pl.

  5. Skip \password TAP test on old IPC::Run versions

  6. Add io_direct setting (developer-only).

  7. Introduce PG_IO_ALIGN_SIZE and align all I/O buffers.

  8. Add palloc_aligned() to allow aligned memory allocations

  9. initdb: When running CREATE DATABASE, use STRATEGY = WAL_COPY.