Simon Riggs wrote:
If we were going to recover from failed-over standby back to original master just via WAL logs we would need all of the WAL files from the point of failover. So you'd need to be storing all WAL file just in case the old master recovers. I can't believe doing that would be the common case, because its so impractical and most people would run out of disk space and need to delete WAL files.
Depends on the transaction volume and database size of course. It's actually not any different from the scenario where the slave goes offline for some reason. You have the the same decision there of how long to keep the WAL files in the master, in case the slave wakes up.
I think we'll need an option to specify a maximum for the number of WAL files to keep around. The DBA should set that to the size of the WAL drive, minus some safety factor.
It should be clear that to make this work you must run with a base backup that was derived correctly on the current master. You can do that by re-copying everything, or you can do that by just shipping changed blocks (rsync etc). So I don't see a problem in the first place.
Hmm, built-in rsync capability would be cool. Probably not in the first phase, though..
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