On 23 March 2017 at 06:42, Simon Riggs <si...@2ndquadrant.com> wrote: > On 23 March 2017 at 01:02, Thomas Munro <thomas.mu...@enterprisedb.com> wrote: > >> Thanks! Please find attached v7, which includes a note we can point >> at when someone asks why it doesn't show 00:00:00, as requested. > > Thanks. > > Now I look harder the handling for logical lag seems like it would be > problematic in many cases. It's up to the plugin whether it sends > anything at all, so we should make a LagTrackerWrite() call only if > the plugin sends something. Otherwise the lag tracker will just slow > down logical replication. > > What I think we should do is add an LSN onto LogicalDecodingContext to > represent the last LSN sent by the plugin, if any. > > If that advances after the call to LogicalDecodingProcessRecord() then > we know we just sent a message and we can track that with > LagTrackerWrite(). > > So we make it the plugin's responsibility to maintain this LSN > correctly, if at all. (It may decide not to) > > In English that means the plugin will update the LSN after each > Commit, and since we reply only on commit this will provide a series > of measurements we can use. It will still give a saw-tooth, but its > better than flooding the LagTracker with false measurements. > > I think it seems easier to add that as a minor cleanup/open item after > this commit.
Second thoughts... I'll just make LagTrackerWrite externally available, so a plugin can send anything it wants to the tracker. Which means I'm explicitly removing the "logical replication support" from this patch. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
