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|0001571: Differential backups for postgresql new plugin
We used the former postgresql plugin from Bareos, and never had this message during backup:
Differential backups are not supported! Only Full and Incremental
This is effectively during a Differential backup. We never had such messages with the old plugin, so we're wondering why we have them now with the Bareos version 23 plugin
Also we wonder, is this hard to support. Isn't the differential simply adding all incrementals into one? We checked old postgresql plugin backups and we have the feeling this also actually just worked correctly.
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After checking how the old plugin behave and especially that to be able to do differential, you will need to have all wal archive present in the right order since last full and we can't warranty that especially as the plugin is not in charge to manage the archive repository.
There's no internal build-in of differential backup in PostgreSQL. The plugin being based on PITR Wal archiving methodology there's no real needs to have a differential level. Full + n number of incremental will allow the restoration to the desired point in time.
As it is specifically linked to the cluster, it also forbidden the use of feature like Virtual Full.
|So you're not simply adding incremental backups together? Since that should work up to the last full otherwise? Or do I oversee something here? :)
Well we provide enough effort I guess to explain what's going on with the plugin in the documentation
And plugin backup are different from traditional file backup.
Well if it wouldn't work, I have to believe you. I was just under the impression that the incremental backups just contain wall data. I checked on the old plugin, and there the differential backups are running fine. If I look into those backups, the differential backups just contain all the backups from the incremental ones. It's very easy, all files seem to be simply present.
So I must be overlooking something, because apparentely, having the exact same wal files as in the incremental backups wouldn't be sufficient? :)
I can't state anything from the screenshot, as the content greatly depend of how checkbox option are checked.
Maybe here I just see the result of full+incremental job merged :-)
No, this was of a single job (unchecked the boxes to merge).
In any case, since it are just wal files that are kept with incremental, wouldn't a differential just work? Or am I missing something in the puzzle?
The old jobs (previous plugin with differential as well) seem to work when we test, but maybe we didn't test the right case or something.
Just a word about this case. The old plugin blindly believe in the fact that all archived wal are there since the full and backup those. If one is missing, the restore will not be possible while the backup would have status "OK".
We decided for the new one to not let user believe the backup was ok when the chance it is not grow as time pass, that's why we disable the Differential mode.
|Also for the incremental we need to make sure we keep enough wall files or otherwise we would have problems? I don't see the big difference differential versus incremental :)
Yes this is not a completely a wrong assumption ;-)
Maybe it would be a good idea to allow differential again, warn in the notes we need long enough wall files, and longterm some safety mechanism would be even better hahaha :)
We do a differential each day , so for us it's really nice to keep the differentials working, it's a great advantage since we take 24 incrementals per day, it's crazy to keep these all for a week long.
So the final statement on our side (of course for the moment, with money or PR everything can be changed :-))
We will not publish the plugin with level D allowed.
But as you know it is quite simple to hack it. So for your own usage you may want to change the M_FATAL to something else line 217
At your own risk.
Differential support will not be enable for this plugin.
Workaround for people knowing the risk they took, can be proposed in a PR and merged afterward if acceptable.
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