Horton

Re: Direct I/O

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Christoph Berg <myon@debian.org>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-04-12T07:37:42Z
Lists: pgsql-hackers 
On Wed, Apr 12, 2023 at 5:48 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Wed, Apr 12, 2023 at 3:04 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> > On Wed, Apr 12, 2023 at 2:56 PM Christoph Berg <myon@debian.org> wrote:
> > > I'm hitting a panic in t_004_io_direct. The build is running on
> > > overlayfs on tmpfs/ext4 (upper/lower) which is probably a weird
> > > combination but has worked well for building everything over the last
> > > decade. On Debian unstable:

After trying a couple of things and doing some googling, it looks like
it's tmpfs that rejects it, not overlayfs, so I'd adjust that commit
message slightly.  Of course it's a completely reasonable thing to
expect the tests to pass (or in this case be skipped) in a tmpfs, eg
/tmp on some distributions.  (It's a strange to contemplate what
O_DIRECT means for tmpfs, considering that it *is* the page cache,
kinda, and I see people have been arguing about that for a couple of
decades since O_DIRECT was added to Linux; doesn't seem that helpful
to me that it rejects it, but 🤷).

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.