Greetings, * Laurenz Albe (laurenz.a...@cybertec.at) wrote: > On Mon, 2021-03-22 at 11:05 -0400, Stephen Frost wrote: > > > Perhaps allowing to set unlogged tables to logged ones without writing WAL > > > is a more elegant way to do that, but I cannot see how that would be any > > > more crash safe than this patch. Besides, the feature doesn't exist yet. > > > > I'm not suggesting it's somehow more crash safe- but it's at least very > > clear what happens in such a case, to wit: the entire table is cleared > > on crash recovery. > > I didn't look at the patch, but are you saying that after changing the > table to LOGGED, it somehow remembers that it is not crash safe and is > emptied if there is a crash before the next checkpoint?
I'm not sure where the confusion is, but certainly once the table has been turned into LOGGED and that's been committed then it should be crash safe, even under 'minimal' with the optimization to avoid actually copying the entire table into the WAL. I don't see any particular reason why that isn't possible to do. Under the proposed 'none', you basically have to throw out the entire cluster on a crash, all because you don't want to use 'UNLOGGED' when you created the tables you want to load data into, or 'TRUNCATE' them in the transaction where you start the data load, either of which gives us enough indication and which we have infrastructure around dealing with in the event of a crash during the load without everything else having to be tossed and everything restored from a backup. That's both a better user experience from the perspective of having fewer WAL levels to understand and from just a general administration perspective so you don't have to go all the way back to a backup to bring the system back up. Thanks, Stephen
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