On Tue, Aug 29, 2017 at 12:13 PM, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: >
Hi Alvaro, > Simone Gotti wrote: > > Hi all, > > > > I noticed that in postgres 10beta3, calling pg_drop_replication_slot on an > > active slot will block until it's released instead of returning an error > > like > > done in pg 9.6. Since this is a change in the previous behavior and the docs > > wasn't changed I made a patch to restore the previous behavior. > > Changing that behavior was the entire point of the cited commit. Sorry, I was thinking that the new behavior was needed for internal future functions since the doc wasn't changed. > > A better fix, from my perspective, is to amend the docs as per the > attached patch. This is what would be useful for logical replication, > which is what replication slots were invented for in the first place. I don't know the reasons why the new behavior is better for logical replication so I trust you. We are using repl slots for physical replication. > If you disagree, let's discuss what other use cases you have, and we can > come up with alternatives that satisfy both. I just faced the opposite problem, in stolon [1], we currently rely on the previous behavior. i.e. we don't want to block waiting for a slot to be released (that under some partitioning conditions could not happen for a long time), but prefer to continue retrying the drop later. Now we partially avoid blocking timing out the drop operation after some seconds. Another idea will be to query the slot status before doing the drop but will lead to a race condition (probably the opposite that that commit was fixing) if the slot is acquired between the query and the drop. > I think a decent answer, > but one which would create a bit of extra churn, would be to have an > optional boolean flag in the command/function for "nowait", instead of > hardcoding either behavior. I think that this will be the best fix. I'm not sure on the policy of these commands and if backward compatibility will be better (in such case the old behavior should be the default and a new "wait" flag could be added). If the default behavior is going to change we have to add different code for postgres >= 10. Thanks, Simone. [1] https://github.com/sorintlab/stolon > > > -- > Álvaro Herrera https://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
