Horton

Re: Direct I/O

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>, 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: 2023-04-14T19:38:29Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2023-04-14 15:21:18 -0400, Tom Lane wrote:
>> +1 for that, though.  (Also, the fact that these animals aren't
>> actually failing suggests that 004_io_direct.pl needs expansion.)

> It's skipped, due to lack of O_DIRECT:
> [20:50:22] t/004_io_direct.pl .............. skipped: no O_DIRECT

Hmm, I'd say that might be just luck.  Whether the compiler honors weird
alignment of locals seems independent of whether the OS has O_DIRECT.

> So perhaps we don't even need a configure test, just a bit of ifdef'ery? It's
> a bit annoying structurally, because the PG*Aligned structs are defined in
> c.h, but the different ways of spelling O_DIRECT are dealt with in fd.h.

> I wonder if we should try to move those structs to fd.h as well...

I doubt they belong in c.h, so that could be plausible; except
I'm not convinced that testing O_DIRECT is sufficient.

			regards, tom lane

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.