Horton

Re: On login trigger: take three

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Daniel Gustafsson <daniel@yesql.se>, Mikhail Gribkov <youzhick@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Greg Nancarrow <gregn4422@gmail.com>, Ivan Panchenko <wao@mail.ru>, Teodor Sigaev <teodor@sigaev.ru>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, vignesh C <vignesh21@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2023-10-12T22:54:01Z
Lists: pgsql-hackers 
On Thu, Oct 12, 2023 at 8:35 PM Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Oct 10, 2023 at 3:43 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> > Yep, in v43 it worked that way.  One transaction has to wait for
> > another finishing update of pg_database tuple, then fails.  This is
> > obviously ridiculous.  Since overlapping setters of flag will have to
> > wait anyway, I changed lock mode in v44 for them to
> > AccessExclusiveLock.  Now, waiting transaction then sees the updated
> > tuple and doesn't fail.
>
> Doesn't that mean that if you create the first login trigger in a
> database and leave the transaction open, nobody can connect to that
> database until the transaction ends?

It doesn't mean that, because when trying to reset the flag v44 does
conditional lock.  So, if another transaction is holding the log we
will just skip resetting the flag.  So, the flag will be cleared on
the first connection after that transaction ends.

------
Regards,
Alexander Korotkov

Commits

  1. Fix some typos in event trigger docs

  2. Use heap_inplace_update() to unset pg_database.dathasloginevt

  3. Remove the flaky check in event_trigger_login regression test

  4. Fix instable 006_login_trigger.pl test

  5. Add support event triggers on authenticated login

  6. Add GUC for temporarily disabling event triggers

  7. Fix typo in reference to __FreeBSD__.

  8. Restore robustness of TAP tests that wait for postmaster restart.

  9. Restore the portal-level snapshot after procedure COMMIT/ROLLBACK.