Re: How to prioritise walsender reading from pg_wal over WAL writes?

On Wed, 2020-11-18 at 11:54 +0000, Alexey Bashtanov wrote:
> If it helps, here's the details of the hardware config.
> The controller is AVAGO MegaRAID SAS 9361-4i,
> the SSDs are INTEL SSDSC2KG960G8 (configured as a raid1).
> Current scheduler used is deadline.
> Currently XFS is mounted without nobarriers, but I'm going to set that when there's high load next time to see how it affects throughput.
>
> Properties of the array
> VD6 Properties :
> ==============
> Strip Size = 256 KB
> Number of Blocks = 1874329600
> VD has Emulated PD = Yes
> Span Depth = 1
> Number of Drives Per Span = 2
> Write Cache(initial setting) = WriteBack
> Disk Cache Policy = Disk's Default
> Encryption = None
> Data Protection = Disabled
> Active Operations = None
> Exposed to OS = Yes
> Creation Date = 28-10-2020
> Creation Time = 05:17:16 PM
> Emulation type = default
> Cachebypass size = Cachebypass-64k
> Cachebypass Mode = Cachebypass Intelligent
> Is LD Ready for OS Requests = Yes
> SCSI NAA Id = 600605b00af03650272c641ca30c3196

Why??

WAL buffers has the most recent information, so that would result in unnecessary delay and I/O.

You'd have to hack the code, but I wonder what leads you to this interesting requirement.

Yours,
Laurenz Albe
--
+43-670-6056265
CYBERTEC PostgreSQL International GmbH
Gröhrmühlgasse 26, A-2700 Wiener Neustadt
Web: https://www.cybertec-postgresql.com