Recently I have asked once again by one of our customers about login trigger in postgres. People are migrating to Postgres from Oracle and looking for Postgres analog of this Oracle feature. This topic is not new:
end even session connect/disconnect hooks were sometimes committed (but then reverted). As far as I understand most of the concerns were related with disconnect hook. Performing some action on session disconnect is actually much more complicated than on login. But customers are not needed it, unlike actions performed at session start.
I wonder if we are really going to make some steps in this directions? The discussion above was finished with "We haven't rejected the concept altogether, AFAICT"
I have tried to resurrect this patch and implement on-connect trigger on top of it. The syntax is almost the same as proposed by Takayuki:
CREATE EVENT TRIGGER mytrigger AFTER CONNECTION ON mydatabase EXECUTE {PROCEDURE | FUNCTION} myproc();
I have replaced CONNECT with CONNECTION because last keyword is already recognized by Postgres and make ON clause mandatory to avoid shift-reduce conflicts.
Actually specifying database name is redundant, because we can define on-connect trigger only for self database (just because triggers and functions are local to the database). It may be considered as argument against handling session start using trigger. But it seems to be the most natural mechanism for users.
On connect trigger can be dropped almost in the same way as normal (on relation) trigger, but with specifying name of the database instead of relation name:
DROP TRIGGER mytrigger ON mydatabase;
It is possible to define arbitrary number of on-connect triggers with different names.
I attached my prototype implementation of this feature. I just to be sure first that this feature will be interested to community. If so, I will continue work in it and prepare new version of the patch for the commitfest.
I have a customer that requires this feature too. Now it uses a solution based on dll session autoloading. Native solution can be great.
