On Thu, Jul 16, 2015 at 6:40 PM, Robert Haas <robertmh...@gmail.com> wrote: > I don't think "the snapshot's LSN" has a well-defined meaning in > general. The obvious meaning would be "the LSN such that all commits > prior to that LSN are visible and all later commits are invisible",
I like this definition. > but such an LSN need not exist. Suppose A writes a commit record at > LSN 0/10000, and then B writes a commit record at 0/10100, and then B > calls ProcArrayEndTransaction(). At this point, B is visible and A is > not visible, even though A's commit record precedes that of B. Maybe that's what Andres referred as "doable with some finicky locking". There is some race conditions to build a snapshot with an associated consistent LSN. If I understand your example, A is supposed to call ProcArrayEndTransaction() anytime soon. Could we wait/lock until it happens? -- Florent -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
