On 2015-01-28 14:54:15 +0000, Kevin Grittner wrote: > Kevin Grittner <kgri...@ymail.com> wrote: > > Alexander Korotkov <aekorot...@gmail.com> wrote: > > >> Could we start snapshot-importing transaction with repeatable > >> read isolation level? > > > > You can if you don't use the option which specifies that you want > > serializable behavior. Why specify --serializable-deferrable if > > you don't? > > > >> AFAICS, they should read exactly same data as snapshot-exporting > >> serializable transaction. > > > > Sort of. The behavior once they have a snapshot and are running is > > the same; the difference is whether the snapshot can see a > > transient state which would not be consistent with some serial > > order of transaction execution. > > Oh, wait; on a re-read I think I may have misunderstood the question. > > If you are talking about having pg_dump acquire a safe snapshot and > have cooperating processes in the same pg_dump run use that > snapshot in repeatable read transactions, then yes -- that would > work. As long as a repeatable read transaction is using a safe > snapshot it will not see any anomalies. That would be a better > solution if it can be done. Do you have any code to suggest, or > should I look at writing it?
Why could it be unsafe to import a snapshot that's been generated as serializable deferrable into another backend? Doesn't the fact that it has been exported out of a deferrable xact that's still running pretty much guarantee that the other xact is also safe? ISTM that the check is just overzelous and/or needs to be moved into ImportSnapshot(). There it then could be made to check if the exporting xact was also deferrable. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
