The only DDL that could affect what partition the row is meant to go into is DROP TABLE or DETACH PARTITION on the partition that's being INSERTed into. In that case, we'll take an AccessExclusiveLock on the partition itself which would prevent the concurrent INSERT.
To me it sounds very much like Martin is trying to use partitioning in a way that's not supported. He didn't mention it, by my guess is he's trying to use a BEFORE INSERT trigger to create a partition that does not exist. That's a very bad idea and he'll be much better off creating the partitions before they're required using some job that runs periodically. I think this is likely the case since otherwise, he'd not have a problem with starting a new transaction to perform the dummy insert to populate the relcache.
If only specific DDL changes invalidate the relcache entry then why not update the cache when -they- happen. I don't understand what is going on behind the scenes so there may be a good explanation.
I am creating missing partition tables ad-hoc roughly once every day as my table naming pattern would suggest, though not as a before insert trigger.
I am inserting about 1000 records every second 24/7, so there will be no "good" time to do the DDL update anyway.
I do not understand how this would not be how partitioned tables where intended to be used, nor why you cannot see the problem of having the first insert statement take a lock on the master table "without my knowledge".
I cannot ensure that a potential dummy insert statement happens before a real insert statement, since having the relcache entry invalidated requires my transaction doing the DDL update to be committed, leaving it all to be a race condition with my normal insert operations.
I'm going to do a workaround to this if not bug then IMO bad design. Probably something along the lines of a more managed table maintenance step. I am fortunate that I can do that. Not everyone will be able to.
I now understand why the lock is taking, which was what I was asking. I thank you for your comments and suggestions.
