On Thu, Sep 10, 2020 at 11:42 AM Dilip Kumar <dilipbal...@gmail.com> wrote: > > On Thu, Sep 10, 2020 at 11:29 AM Amit Kapila <amit.kapil...@gmail.com> wrote: >> >> Hi, >> >> There is a recent build farm failure [1] in one of the test_decoding >> tests as pointed by Tom Lane [2]. The failure report is shown below: >> >> @@ -71,6 +71,8 @@ >> data >> ------------------------------------------ >> opening a streamed block for transaction >> + closing a streamed block for transaction >> + opening a streamed block for transaction >> streaming change for transaction >> streaming change for transaction >> streaming change for transaction >> @@ -83,7 +85,7 @@ >> streaming change for transaction >> closing a streamed block for transaction >> committing streamed transaction >> -(13 rows) >> +(15 rows) >> >> Here, the symptoms are quite similar to what we have fixed in commit >> 82a0ba7707 which is that an extra empty transaction is being decoded >> in the test. It can happen even if have instructed the test to 'skip >> empty xacts' for streaming transactions because the test_decoding >> plugin APIs (related to streaming changes for in-progress xacts) makes >> no effort to skip such empty xacts. It was kept intentionally like >> that under the assumption that we would never try to stream empty >> xacts but on closer inspection of the code, it seems to me that >> assumption was not correct. Basically, we can pick to stream a >> transaction that has change messages for >> REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT and we don't send such >> messages to downstream rather they are just to update the internal >> state. So, in this particular failure, it is possible that autovacuum >> transaction has got such a change message added by one of the other >> committed xact and on trying to stream it we get such additional >> messages. The fix is to skip empty xacts when indicated by the user in >> streaming APIs of test_decoding. >> >> Thoughts? > > > Yeah, that's an issue. > >> >> >> [1] - >> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skink&dt=2020-09-09+03%3A42%3A19 >> [2] - https://www.postgresql.org/message-id/118303.1599691636%40sss.pgh.pa.us >> > > I have written a test case to reproduce the same. I have also prepared a > patch to skip the empty transaction. And after that, the issue has been > fixed. But the extra side effect will be that it would skip any empty stream > even if the transaction is not empty. As such I don't see any problem with > that but this is not what the user has asked for. >
Isn't that true for non-streaming xacts as well? Basically skip-empty-xacts option indicates that if there is no change for 'tuple' or 'message', we skip it. -- With Regards, Amit Kapila.
