Re: How to prioritise walsender reading from pg_wal over WAL writes?
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 Best, Alex
Re: How to prioritise walsender reading from pg_wal over WAL writes?
On Wed, 2020-11-18 at 11:54 +, 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
Re: How to prioritise walsender reading from pg_wal over WAL writes?
Sorry Laurenz, My reply did not get threaded appropriately. My original question was here: https://www.postgresql.org/message-id/a74d5732-60fd-d18b-05fd-7b2b97099f19%40imap.cc I'd like to prioritize walsender for replication not to lag too much. Otherwise, when I have load spikes on master, standby lags, sometimes by hundreds of gigabytes. Best, Alex
Re: How to prioritise walsender reading from pg_wal over WAL writes?
On Wed, 2020-11-18 at 12:15 +, Alexey Bashtanov wrote: > My reply did not get threaded appropriately. > My original question was here: > https://www.postgresql.org/message-id/a74d5732-60fd-d18b-05fd-7b2b97099f19%40imap.cc > I'd like to prioritize walsender for replication not to lag too much. > Otherwise, when I have load spikes on master, standby lags, sometimes by > hundreds of gigabytes. I would first determine where the bottleneck is. Is it really the walsender, or is it on the network or in the standby server's replay? Check the difference between "sent_lsn", "replay_lsn" from "pg_stat_replication" and pg_current_wal_lsn() on the primary. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
