On May 29, 2017 12:21:50 PM PDT, Petr Jelinek <petr.jeli...@2ndquadrant.com> wrote: >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.
That's precisely what I pointed out a few emails above, and what I suggest changing. Andres -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
