On 2017-05-01 03:54:49 +0200, Petr Jelinek wrote: > I agree with adding running, I think that's good thing even for the per > transaction tracking and snapshot exports - we could use the newly added > field to get rid of the issue we have with 'snapshot too large' when > there were many aborted transactions while we waited for running ones to > finish.
I'm not sure of that - what I was proposing would only track this for the ->running substructure. How'd that help? > But, I still think we need to restart the tracking after new > xl_running_xacts. Reason for that is afaics any of the catalog snapshots > that we assigned to transactions at the end of SnapBuildCommitTxn might > be corrupted otherwise as they were built before we knew one of the > supposedly running txes was actually already committed and that > transaction might have done catalog changes. I'm afraid you're right. But I think this is even more complicated: The argument in your version that this can only happen once, seems to also be holey: Just imagine a pg_usleep(3000 * 1000000) right before ProcArrayEndTransaction() and enjoy the picture. Wonder if we should just (re-)add a stage between SNAPBUILD_START and SNAPBUILD_FULL_SNAPSHOT. Enter SNAPBUILD_BUILD_INITIAL_SNAPSHOT at the first xl_running_xacts, wait for all transactions to end with my approach, while populating SnapBuild->committed, only then start collecting changes for transactions (i.e. return true from SnapBuildProcessChange()), return true once all xacts have finished again. That'd presumably be a bit easier to understand, more robust - and slower. - Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
