On 2015-07-16 12:40:07 -0400, Robert Haas wrote: > On Wed, Jul 15, 2015 at 12:51 PM, Florent Guiliani <flor...@guiliani.fr> > wrote: > > During slot creation, the snapshot building and exporting code seems > > highly coupled with the logical decoding stuff. It doesn't seems much > > reusable to retrieve the snapshot's LSN outside of logical decoding. > > 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", > 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.
Well, in combination with logical decoding it kinda has one: It should allow you to take a dump of the database with a certain snapshot and replay all transactions with a commit lsn bigger than the "snapshot's lsn" and end up with a continually consistent database. Visibility for HS actually works precisely in commit LSN order, even if that is possibly different than on the primary... -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
