Re: On login trigger: take three

From: Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: On login trigger: take three
Date: 2020-09-14 14:12:42
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On 14.09.2020 12:44, Pavel Stehule wrote:
> Hi
> I am checking last patch, and there are notices
> 1. disable_session_start_trigger should be SU_BACKEND instead SUSET
> 2. The documentation should be enhanced - there is not any note about
> behave when there are unhandled exceptions, about motivation for this
> event trigger
> 3. regress tests should be enhanced - the cases with exceptions are
> not tested
> 4. This trigger is not executed again after RESET ALL or DISCARD ALL -
> it can be a problem if somebody wants to use this trigger for
> initialisation of some session objects with some pooling solutions.
> 5. The handling errors don't work well for canceling. If event trigger
> waits for some event, then cancel disallow connect although connected
> user is superuser
> $$ begin perform pg_sleep(10000); raise notice '%', fx1(100);raise
> notice 'kuku kuku'; end  $$ language plpgsql;
> probably nobody will use pg_sleep in this routine, but there can be
> wait on some locks ...
> Regards
> Pavel

Thank you very much for looking at my patch for connection triggers.
I have fixed 1-3 issues in the attached patch.
Concerning 4 and 5 I have some doubts:

4. Should I add some extra GUC to allow firing of session_start trigger
in case of  RESET ALL or DISCARD ALL ?
Looks like such behavior contradicts with event name "session_start"...
And do we really need it? If some pooler is using RESET ALL/DISCARD ALL
to emulate session semantic then  most likely it provides way to define
custom actions which
should be perform for session initialization. As far as I know, for
example pgbouncer allows do define own on-connect hooks.

5. I do not quite understand your concern. If I define  trigger
procedure which is  blocked (for example as in your example), then I can
use pg_cancel_backend to interrupt execution of login trigger and
superuser can login. What should be changed here?

Konstantin Knizhnik
Postgres Professional:
The Russian Postgres Company

Attachment Content-Type Size
on_connect_event_trigger-7.patch text/x-patch 16.5 KB

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