Horton

Re: Direct I/O

Andrew Dunstan <andrew@dunslane.net>

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From: Andrew Dunstan <andrew@dunslane.net>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Heikki Linnakangas <hlinnaka@iki.fi>, Noah Misch <noah@leadboat.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, pgsql-hackers@postgresql.org
Date: 2023-04-09T16:35:29Z
Lists: pgsql-hackers 
On 2023-04-09 Su 09:14, Andrew Dunstan wrote:
>
>
> On 2023-04-09 Su 08:39, Thomas Munro wrote:
>> On Sun, Apr 9, 2023 at 11:25 PM Andrew Dunstan<andrew@dunslane.net>  wrote:
>>> Didn't seem to make any difference.
>> Thanks for testing.  I think it's COW (and I think that implies also
>> checksums?) that needs to be turned off, at least based on experiments
>> here.
>
>
>
> Googling agrees with you about checksums.  But I'm still wondering if 
> we shouldn't disable COW for the build directory etc. It is suggested 
> at [1]:
>
>
>     Recommend to set nodatacow – turn cow off – for the files that
>     require fast IO and tend to get very big and get alot of random
>     writes: such VMDK (vm disks) files and the like.
>
>
> I'll give it a whirl.
>
>

with COW disabled, I can no longer generate a failure with the test.


cheers


andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com

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.