Обсуждение: shared buffers and startup process
Hi,
I have a master slave setup with streaming replication.
I have a lots of wal files that were moved from master but not applied yet , a big delay in the replica.
The replica is not working on hotstandby mode , no conflicts to delay wals apply on it.
I would like to know if increasing the amount of shared-buffers could help the startup process applying the wals. I would like to know if in the process of reading the wals and applying them, blocks that should be written will be brought to shared buffer or not?? If yes, having a bigger shared buffer will keep as much as possible the amount of pages there and increase the startup process's speed avoiding pages's replacement and going to the OS cache and maybe to the disk .
Does it make sense?
Thanks in advanced.
Regards,
Joao
On Tue, Jan 14, 2020 at 04:29:51PM +0100, Joao Junior wrote: > I would like to know if increasing the amount of shared-buffers could help > the startup process applying the wals. I would like to know if in > the process of reading the wals and applying them, blocks that should be > written will be brought to shared buffer or not?? Please feel free to look at XLogReadBufferForRedo() in xlogutils.c and check what the routine does, and when/where it gets called. The code is well-documented, so you will find your answer easily. > If yes, having a bigger > shared buffer will keep as much as possible the amount of pages there and > increase the startup process's speed avoiding pages's replacement and going > to the OS cache and maybe to the disk . > Does it make sense? It does. Even if relying on the OS cache would be enough in most cases, it is good to keep a certain of pages hot enough, and you need to be careful with not setting shared_buffers too high either. -- Michael