Horton

Re: Direct I/O

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>, 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@postgresql.org
Date: 2023-05-01T02:47:57Z
Lists: pgsql-hackers

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On Mon, May 1, 2023 at 12:00 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Justin Pryzby <pryzby@telsasoft.com> writes:
> > On Sun, Apr 30, 2023 at 06:35:30PM +1200, Thomas Munro wrote:
> >> What about a
> >> warning message about that at startup if it's on?
>
> > Such a warning wouldn't be particularly likely to be seen by someone who
> > already didn't read/understand the docs for the not-feature that they
> > turned on.
>
> Yeah, I doubt that that would be helpful at all.

Fair enough.

> > Since this is -currently- a developer-only feature, it seems reasonable
> > to rename the GUC to debug_direct_io, and (at such time as it's
> > considered to be helpful to users) later rename it to direct_io.
>
> +1

Yeah, the future cross-version confusion thing is compelling.  OK,
here's a rename patch.  I left all the variable names and related
symbols as they were, so it's just the GUC that gains the prefix.  I
moved the documentation hunk up to be sorted alphabetically like
nearby entries, because that seemed to look nicer, even though the
list isn't globally sorted.

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.