Re: WAL replay is too slow on secondary server

On Thu, 2025-10-30 at 10:06 +0530, OMPRAKASH SAHU wrote:
> We have a postgresql cluster setup using patroni.
> The DB is being used for heavy transactional application, now the problem is that on replica server WAL replay is too
slow.
> We have increased the IOPS to 6k and Throughput to 600 on nvme EBS volume of wal directory and 10k &800 on data
directory.
>
> but the WAL is being accumulated on the replica as usual and applying wal is having no improvement.
> changed the maintenance_io_concurrency on replica to 32.
> CPU utilization max=20% , RAM utilization is also max 20.

Is the disk saturated?

> I would request your thoughts and suggestions if we can get rid of this slowness and get some speed.

WAL replay during streaming replication is single-threaded.
So you can only use a faster CPU or disk, depending on what is the bottleneck.
Perhaps your shared buffers are too small, and you have cache contention.

Yours,
Laurenz Albe