Robert Treat wrote:
1) Alert if checkpointing stops occuring within a reasonable time frame (note
there are failure cases and normal use cases where this might occur) (also
note I'll agree, this isn't common, but the results are pretty disatrous if
it does happen)
What are the normal use cases where this would occur? I can't think of any.
Wrt. failure cases, there's a million things that can go wrong in a
system, and only few of them will give the symptom of "checkpoints
stopped happening", so I'm not excited about adding a facility to
monitor just that.
More hooks for monitoring purposes in general would be nice, and I would
like to see them exposed as SQL functions, but I'd like to see a much
bigger proposal for that.
2) Can be graphed over time (using rrdtool and others) for trending checkpoint
Hmm. You'd need the historical data to do that properly. In particular,
if two checkpoints happen between the polling interval, you'd miss that.
log_checkpoints=on, in CSV output, seems like a better approach for that.
3) Ease monitoring of checkpoints across pitr setups
How is that different from monitoring in a non-pitr setup?
4) Help determine if your checkpoints are being timeout driven or segment
driven, or if you need to look at those settings
Seems like the log_checkpoints output is more useful for that, as it
directly tells you what triggered the checkpoint.
5) Determine the number of log files that will need to be replayed in the
event of a crash
If you have a requirement for that, just set checkpoint_segments
accordingly. And again, you can get the information in the logs by
6) Helps give an indication on if you should enter a manual checkpoint before
issuing a pg_start_backup call
If you want the backup to begin immediately, just do a manual checkpoint
unconditionally. It'll finish quickly if there hasn't been much activity
since the last one. We talked about adding a new variant of
pg_start_backup() that does that automatically (or rather, just hurries
the current checkpoint) in the 8.3 cycle, but didn't do it in the end.
Perhaps we should add that, after all?
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