Craig Ringer wrote: > Hi all > > I think I found a couple of logical decoding issues while writing tests for > failover slots. > > Despite the docs' claim that a logical slot will replay data "exactly > once", a slot's confirmed_lsn can go backwards and the SQL functions can > replay the same data more than once.We don't mark a slot as dirty if only > its confirmed_lsn is advanced, so it isn't flushed to disk. For failover > slots this means it also doesn't get replicated via WAL. After a master > crash, or for failover slots after a promote event, the confirmed_lsn will > go backwards. Users of the SQL interface must keep track of the safely > locally flushed slot position themselves and throw the repeated data away. > Unlike with the walsender protocol it has no way to ask the server to skip > that data. > > Worse, because we don't dirty the slot even a *clean shutdown* causes slot > confirmed_lsn to go backwards. That's a bug IMO. We should force a flush of > all slots at the shutdown checkpoint, whether dirty or not, to address it.
Why don't we mark the slot dirty when confirmed_lsn advances? If we fix that, doesn't it fix the other problems too? -- Álvaro Herrera 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
