On Tue, Jun 21, 2022 at 1:07 PM Kirill Reshke <reshke@double.cloud> wrote: > > Recently we faced a problem with one of our production clusters. We use a > cascade replication setup in this cluster, that is: master, standby (r1), and > cascade standby (r2). From time to time, the replication lag on r1 used to > grow, while on r2 it did not. Analysys showed that r1 startup process was > spending a lot of time in reading wal from disk. Increasing > /sys/block/md2/queue/read_ahead_kb to 16384 (from 0) helps in this case. > Maybe we can add fadvise call in postgresql startup, so it would not be > necessary to change settings on the hypervisor? >
I wonder if the newly introduced "recovery_prefetch" [1] for PG-15 can help your case? [1] - https://www.postgresql.org/docs/devel/runtime-config-wal.html#RUNTIME-CONFIG-WAL-RECOVERY -- With Regards, Amit Kapila.
