On 2020/11/25 13:47, Michael Paquier wrote:
On Wed, Nov 25, 2020 at 01:07:47AM +0000, tsunakawa.ta...@fujitsu.com wrote:
From: Bossart, Nathan <bossa...@amazon.com>
It may be useful for backups taken with the "consistent snapshot"
approach. As noted in the documentation [0], running CHECKPOINT
before taking the snapshot can reduce recovery time. However, users
might wish to avoid the IO spike caused by an immediate checkpoint.
[0] https://www.postgresql.org/docs/devel/backup-file.html
Ah, understood. I agree that the slow or spread manual checkpoint is good to
have.
I can see the use case for IMMEDIATE, but I fail to see the use cases
for WAIT and FORCE. CHECKPOINT_FORCE is internally implied for the
end-of-recovery and shutdown checkpoints. WAIT could be a dangerous
thing if disabled, as clients could pile up requests to the
checkpointer for no real purpose.
We may want to disable WAIT (or specify wait timeout?) when doing
checkpoint with IMMEDIATE disabled, to avoid long-running command.
OTOH, if we support WAIT disabled, I'd like to have the feature to see
whether the checkpoint has been completed or not. We can do that
by using log_checkpoints, but that's not convenient.
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
