On 29/05/17 20:59, Andres Freund wrote: > > > On May 29, 2017 11:58:05 AM PDT, Petr Jelinek <petr.jeli...@2ndquadrant.com> > wrote: >> On 27/05/17 17:17, Andres Freund wrote: >>> >>> >>> On May 27, 2017 9:48:22 AM EDT, Petr Jelinek >> <petr.jeli...@2ndquadrant.com> wrote: >>>> Actually, I guess it's the pid 47457 (COPY process) who is actually >>>> running the xid 73322726. In that case that's the same thing >> Masahiko >>>> Sawada reported [1]. Which basically is result of snapshot builder >>>> waiting for transaction to finish, that's normal if there is a long >>>> transaction running when the snapshot is being created (and the COPY >> is >>>> a long transaction). >>> >>> Hm. I suspect the issue is that the exported snapshot needs an xid >> for some crosscheck, and that's what we're waiting for. Could you >> check what happens if you don't assign one and just content the error >> checks out? Not at my computer, just theorizing. >>> >> >> I don't think that's it, in my opinion it's the parallelization of >> table >> data copy where we create snapshot for one process but then the next >> one >> has to wait for the first one to finish. Before we fixed the >> snapshotting, the second one would just use the ondisk snapshot so it >> would work fine (except the snapshot was corrupted of course). I wonder >> if we could somehow give it a hint to ignore the read-only txes, but >> then we have no way to enforce the txes to stay read-only so it does >> not >> seem safe. > > Read-only txs have no xid ... >
That's what I mean by hinting, normally they don't but building initial snapshot in snapshot builder calls GetTopTransactionId() (see SnapBuildInitialSnapshot()) which will assign it xid. -- Petr Jelinek 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
