Ants, * Ants Aasma (ants.aa...@eesti.ee) wrote: > On Jun 13, 2013 4:18 AM, "Stephen Frost" <sfr...@snowman.net> wrote: > > * Ants Aasma (a...@cybertec.at) wrote: > > > In a cluster setting you take the CSN value on the master, then before > > > starting execution on a standby you wait until that the standby has > > > replayed enough WAL to reach the CSN point read from the master and > > > you know that after that everything that the snapshot can see is also > > > replayed on the standby. > > > > This does make a lot of sense- but to clarify, this would only be for > > certain isolation levels, right? Or would we implement this for every > > snapshot taken in a read-committed transaction? > > I don't see a way how snapshots representing different points in time could > provide sensible results for parallel queries, so this needs to be used for > all snapshots.
To be honest, I had really looked at this out of context and was
thinking of it being used with replication and hot-standbys. I agree
that you'd have to use this for all snapshots if you're using it for
parallel query execution.
> This is why having the capability to request for a snapshot
> that is fresh enough for a specific client but old enough to not require
> replication waits would be a good feature.
That's an interesting concept.
Thanks,
Stephen
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