On Thu, Jun 25, 2015 at 04:02:33PM +0000, BRUSSER Michael wrote: > Some time ago we upgraded from v. 8.4.4 to 9.4.0 and we are seeing errors in > some regression tests. > > LOCATION: exec_simple_query, postgres.c:887 > ERROR: 40001: could not serialize access due to read/write dependencies > among transactions
Would you be so kind as to send along a way to reproduce the problem you are seeing, ideally a minimal one? > The database at this point is likely to have a barrage of read and write ops > against few tables. > I understand that using serializable transaction we probably should be ready > to retry, Yes > but it would be helpful to understand why we did not see so many errors in > the past. Changing the transaction isolation level, which was mislabeled "serializable" in 8.4 but was actually snapshot isolation, can produce differences. https://en.wikipedia.org/wiki/Snapshot_isolation > Did something changed from 8.4.4 to 9.4.0? Yes. 9.1 introduced SSI, which added serialization checks to the snapshot isolation that existed before. https://wiki.postgresql.org/wiki/SSI > Maybe Postgres has more aggressive predicate locking mechanism now? > Can it be that because of the small table size it performs sequential scan > and locks the entire table? > > Sorry if any of these questions are plain stupid. Thanks for asking. These questions are quite reasonable. Cheers, David. -- David Fetter <da...@fetter.org> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fet...@gmail.com Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
