On Mon, Sep 25, 2017 at 6:57 PM, Thomas Munro <thomas.mu...@enterprisedb.com > wrote:
> On Mon, Sep 25, 2017 at 8:37 PM, Haribabu Kommi > <kommi.harib...@gmail.com> wrote: > > After I tune the GUC to go with sequence scan, still I am not getting the > > error > > in the session-2 for update operation like it used to generate an error > for > > parallel > > sequential scan, and also it even takes some many commands until unless > the > > S1 > > commits. > > Hmm. Then this requires more explanation because I don't expect a > difference. I did some digging and realised that the error detail > message "Reason code: Canceled on identification as a pivot, during > write." was reached in a code path that requires > SxactIsPrepared(writer) and also MySerializableXact == writer, which > means that the process believes it is committing. Clearly something > is wrong. After some more digging I realised that > ParallelWorkerMain() calls EndParallelWorkerTransaction() which calls > CommitTransaction() which calls > PreCommit_CheckForSerializationFailure(). Since the worker is > connected to the leader's SERIALIZABLEXACT, that finishes up being > marked as preparing to commit (not true!), and then the leader get > confused during that write, causing a serialization failure to be > raised sooner (though I can't explain why it should be raised then > anyway, but that's another topic). Oops. I think the fix here is > just not to do that in a worker (the worker's CommitTransaction() > doesn't really mean what it says). > > Here's a version with a change that makes that conditional. This way > your test case behaves the same as non-parallel mode. > With the latest patch, I didn't find any problems. > > I will continue my review on the latest patch and share any updates. > > Thanks! The patch looks good, and I don't have any comments for the code. The test that is going to add by the patch is not generating a true parallelism scenario, I feel it is better to change the test that can generate a parallel sequence/index/bitmap scan. Regards, Hari Babu Fujitsu Australia
