Horton

Re: Direct I/O

Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>

View thread View on postgr.es
From: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Christoph Berg <myon@debian.org>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-04-12T13:31:26Z
Lists: pgsql-hackers 
Thomas Munro <thomas.munro@gmail.com> writes:

> I think I have that working OK.  Any Perl hackers want to comment on
> my use of IO::File (copied from examples on the internet that showed
> how to use O_DIRECT)?  I am not much of a perl hacker but according to
> my package manager, IO/File.pm came with perl itself.

Indeed, and it has been since perl 5.003_07, released in 1996.  And Fcntl
has known about O_DIRECT since perl 5.6.0, released in 2000, so we can
safely use both.

> And the Fcntl eval trick that I copied from File::stat, and the
> perl-critic suppression that requires?
[…]
> +	no strict 'refs';    ## no critic (ProhibitNoStrict)
> +	my $val = eval { &{'Fcntl::O_DIRECT'} };
> +	if (defined $val)

This trick is only needed in File::stat because it's constructing the
symbol name dynamically.  And because Fcntl by default exports all the
O_* and F_* constants it knows about, we can simply do:

   	if (defined &O_DIRECT)
> +	{
> +		use Fcntl qw(O_DIRECT);

The `use Fcntl;` above will already have imported this, so this is
redundant.

- ilmari

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.