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: Andres Freund <andres@anarazel.de>
Cc: Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, Noah Misch <noah@leadboat.com>, Andrew Dunstan <andrew@dunslane.net>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Euler Taveira <euler.taveira@enterprisedb.com>
Date: 2024-11-07T20:11:46Z
Lists: pgsql-hackers 
On Thu, Nov 7, 2024 at 11:41 AM Andres Freund <andres@anarazel.de> wrote:
> I think the patch should not be merged as-is. It's just too ugly and fragile.

Understood; I'm trying to find a way forward, and I'm pointing out
that the alternatives I've tried seem to me to be _more_ fragile.

Are there any items in this list that you disagree with/are less
concerned about?

- the pre-auth step must always initialize the entire pgstat struct
- two-step initialization requires two PGSTAT_BEGIN_WRITE_ACTIVITY()
calls for _every_ backend
- two-step initialization requires us to couple against the order that
authentication information is being filled in (pre-auth, post-auth, or
both)

> I think it might make more sense to use pgstat_report_activity() or such here,
> rather than using wait events to describe something that's not a wait.

I'm not sure why you're saying these aren't waits. If pam_authenticate
is capable of hanging for hours and bringing down a production system,
is that not a "wait"?

> > I agree that would be amazing! I'm not about to tackle reliable
> > interrupts for all of the current blocking auth code for v18, though.
> > I'm just trying to make it observable when we do something that
> > blocks.
>
> Well, with that justification we could end up adding wait events for large
> swaths of code that might not actually ever wait.

If it were hypothetically useful to do so, would that be a problem?
I'm trying not to propose things that aren't actually useful.

--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