Horton

Re: Direct I/O

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Noah Misch <noah@leadboat.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: 2023-04-30T22:11:48Z
Lists: pgsql-hackers

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On Sun, Apr 30, 2023 at 6:35 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Sun, Apr 30, 2023 at 4:11 PM Noah Misch <noah@leadboat.com> wrote:
> > 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_?
>
> Hmm, yeah I think people coming from other databases would be tempted
> by it.  But, unlike the
> please-jam-a-gather-node-on-top-of-the-plan-so-I-can-debug-the-parallel-executor
> switch, I think of this thing more like an experimental feature that
> is just waiting for more features to make it useful.  What about a
> warning message about that at startup if it's on?

Something like this?  Better words welcome.

$ ~/install//bin/postgres -D pgdata -c io_direct=data
2023-05-01 09:44:37.460 NZST [99675] LOG:  starting PostgreSQL 16devel
on x86_64-unknown-freebsd13.2, compiled by FreeBSD clang version
14.0.5 (https://github.com/llvm/llvm-project.git
llvmorg-14.0.5-0-gc12386ae247c), 64-bit
2023-05-01 09:44:37.460 NZST [99675] LOG:  listening on IPv6 address
"::1", port 5432
2023-05-01 09:44:37.460 NZST [99675] LOG:  listening on IPv4 address
"127.0.0.1", port 5432
2023-05-01 09:44:37.461 NZST [99675] LOG:  listening on Unix socket
"/tmp/.s.PGSQL.5432"
2023-05-01 09:44:37.463 NZST [99675] WARNING:  io_direct is an
experimental setting for developer testing only
2023-05-01 09:44:37.463 NZST [99675] HINT:  File I/O may be
inefficient or not work on some file systems.
2023-05-01 09:44:37.465 NZST [99678] LOG:  database system was shut
down at 2023-05-01 09:43:51 NZST
2023-05-01 09:44:37.468 NZST [99675] LOG:  database system is ready to
accept connections

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.