Horton

Re: [PATCH] pg_stat_activity: make slow/hanging authentication more visible

Jacob Champion <jacob.champion@enterprisedb.com>

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From: Jacob Champion <jacob.champion@enterprisedb.com>
To: Noah Misch <noah@leadboat.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Euler Taveira <euler.taveira@enterprisedb.com>
Date: 2024-07-08T21:09:21Z
Lists: pgsql-hackers

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On Sun, Jun 30, 2024 at 10:48 AM Noah Misch <noah@leadboat.com> wrote:
> That looks like a reasonable user experience.  Is any field newly-nullable?

Technically I think the answer is no, since backends such as walwriter
already have null database and user fields. It's new for a client
backend to have nulls there, though.

> That said, it
> may be more fruitful to arrange for authentication timeout to cut through PAM
> etc.

That seems mostly out of our hands -- the misbehaving modules are free
to ignore our signals (and do). Is there another way to force the
issue?

> Hanging connection slots hurt even if they lack an xmin.

Oh, would releasing the xmin not really move the needle, then?

> I assume it
> takes an immediate shutdown to fix them?

That's my understanding, yeah.

> > Would anyone like me to be more aggressive, and create a pgstat entry
> > as soon as we have the opening transaction? Or... as soon as a
> > connection is made?
>
> All else being equal, I'd like backends to have one before taking any lmgr
> lock or snapshot.

I can look at this for the next patchset version.

> > I haven't decided how to test these patches. Seems like a potential
> > use case for injection points, but I think I'd need to preload an
> > injection library rather than using the existing extension. Does that
> > seem like an okay way to go?
>
> Yes.

I misunderstood how injection points worked. No preload module needed,
so v2 adds a waitpoint and a test along with a couple of needed tweaks
to BackgroundPsql. I think 0001 should probably be applied
independently.

Thanks,
--Jacob

Commits

  1. Fix race condition in TAP test 007_pre_auth

  2. Split pgstat_bestart() into three different routines

  3. backport: Extend background_psql() to be able to start asynchronously

  4. backport: Improve handling of empty query results in BackgroundPsql

  5. Improve handling of empty query results in BackgroundPsql::query()

  6. Extend Cluster.pm's background_psql() to be able to start asynchronously

  7. dblink: Replace WAIT_EVENT_EXTENSION with custom wait events