Re: Backup Question

> So you can grab the extra files, but you can't make it apply them,
> as you are telling it that it doesn't need to.

Do I have to, though? Replaying transaction logs is baked into the crash recovery system. If I interrupt it in the middle of a checkpoint, it should be able to revert to the previous checkpoint that did succeed. By including the extra WAL files, it would re-apply them, just like in a crash recovery.

Of course, that only works if I interrupt it by shutting the replica down. By backing up across a checkpoint, I run the risk of a race condition where some files were backed up before the checkpoint, and others afterwards. Which raises the question: isn't that risk the same with a regular backup? The database doesn't just stop checkpointing because a backup is in progress. There must be some internal detail I'm missing.

Either way, I'll add a routine to stall the standby backup until the restartpoint corresponding to the pg_start_backup has been replayed. I'll see if that helps.

Thanks!

--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd | Suite 500 | Chicago IL, 60604
312-676-8870
sthomas(at)optionshouse(dot)com

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