Re: Direct I/O

Andrew Dunstan <andrew@dunslane.net>

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: 2023-04-09T13:14:28Z

Lists: pgsql-hackers

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.


cheers


andrew


[1] <http://www.infotinks.com/btrfs-disabling-cow-file-directory-nodatacow/>

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

Commits

Rename hook functions for debug_io_direct to match variable name.
- 155c81463c26 16.0 landed
- 4f3514f201cf 17.0 landed
Rename io_direct to debug_io_direct.
- 319bae9a8da6 16.0 landed
Skip the 004_io_direct.pl test if a pre-flight check fails.
- 6ca8df2d6147 16.0 landed
Use higher wal_level for 004_io_direct.pl.
- 980e8879f54a 16.0 landed
Skip \password TAP test on old IPC::Run versions
- 2e57ffe12f6b 16.0 cited
Add io_direct setting (developer-only).
- d4e71df6d757 16.0 landed
Introduce PG_IO_ALIGN_SIZE and align all I/O buffers.
- faeedbcefd40 16.0 landed
Add palloc_aligned() to allow aligned memory allocations
- 439f61757f05 16.0 cited
initdb: When running CREATE DATABASE, use STRATEGY = WAL_COPY.
- ad43a413c4f7 15.0 cited