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: Thomas Munro <thomas.munro@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>, Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>, Christoph Berg <myon@debian.org>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-04-14T17:21:33Z
Lists: pgsql-hackers 
Since the direct I/O commit went in, buildfarm animals
curculio and morepork have been issuing warnings like

hashpage.c: In function '_hash_expandtable':
hashpage.c:995: warning: ignoring alignment for stack allocated 'zerobuf'

in places where there's a local variable of type PGIOAlignedBlock
or PGAlignedXLogBlock.  I'm not sure why only those two animals
are unhappy, but I think they have a point: typical ABIs don't
guarantee alignment of function stack frames to better than
16 bytes or so.  In principle the compiler could support a 4K
alignment request anyway by doing the equivalent of alloca(3),
but I do not think we can count on that to happen.

			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.