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Re: Refactoring postmaster's code to cleanup after child exit

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Andres Freund <andres@anarazel.de>, Noah Misch <noah@leadboat.com>, Michael Paquier <michael@paquier.xyz>
Cc: Tomas Vondra <tomas@vondra.me>, Thomas Munro <thomas.munro@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2025-03-06T20:49:20Z
Lists: pgsql-hackers

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In short, all the 4 patches look good to me. Thanks for picking this up!

On 06/03/2025 22:16, Andres Freund wrote:
> On 2025-03-05 20:49:33 -0800, Noah Misch wrote:
>>> This behaviour makes it really hard to debug problems. It'd have been a lot
>>> easier to understand the problem if we'd seen psql's stderr before the test
>>> died.
>>>
>>> I guess that mean at the very least we'd need to put an eval {} around the
>>> ->pump() call., print $self->{stdout}, ->{stderr} and reraise an error?
>>
>> That sounds right.
> 
> In the attached patch I did that for wait_connect().  I did verify that it
> works by implementing the wait_connect() fix before fixing
> 002_connection_limits.pl, which fails if a sleep(1) is added just before the
> proc_exit(1) for FATAL.

+1. For the archives sake, I just want to clarify that this pump stuff 
is all about getting better error messages on a test failure. It doesn't 
help with the original issue.

This is all annoyingly complicated, but getting good error messages is 
worth it.

> On 2025-03-05 08:23:32 +0900, Michael Paquier wrote:>> Why not adding an injection point with a WARNING or a LOG generated, 
then
>> check the server logs for the code path taken based on the elog() generated
>> with the point name?
> 
> I think the log_min_messages approach is a lot simpler. If we need something
> like this more widely we can reconsider injection points...

+1. It's a little annoying to depend on a detail like the "client 
backend process exited" debug message, but seems like the best fix for now.

> I also attached a patch to improve connect_fails()/connect_ok() test names a
> bit. They weren't symmetric and I felt they were lacking in detail for the
> psql return code check.

+1.

While we're at it, attached are a few more cleanups I noticed.

> Another annoying and also funny problem I saw is this failure:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skink&dt=2025-03-06%2009%3A18%3A21
> 2025-03-06 10:42:02.552 UTC [372451][postmaster][:0] LOG:  1800 s is outside the valid range for parameter "authentication_timeout" (1 s .. 600 s)
> 
> I had to increase PG_TEST_TIMEOUT_DEFAULT due to some other test timing out
> when run under valgrind (due to having to insert a lot of rows). But then this
> test runs into the above issue.
> 
> The easiest way seems to be to just limit PG_TEST_TIMEOUT_DEFAULT in this
> test.

LGTM

-- 
Heikki Linnakangas
Neon (https://neon.tech)

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix test name and username used in failed connection attempts

  2. tests: Don't fail due to high default timeout in postmaster/003_start_stop

  3. tests: Fix race condition in postmaster/002_connection_limits

  4. Pass MyPMChildSlot as an explicit argument to child process

  5. Assign a child slot to every postmaster child process

  6. Kill dead-end children when there's nothing else left

  7. Replace postmaster.c's own backend type codes with BackendType

  8. Use an shmem_exit callback to remove backend from PMChildFlags on exit

  9. Add test for dead-end backends

  10. Add test for connection limits

  11. Fix garbled process name on backend crash

  12. Consolidate postmaster code to launch background processes

  13. Fix comment on processes being kept over a restart

  14. Refactor code to handle death of a backend or bgworker in postmaster

  15. Make BackgroundWorkerList doubly-linked

  16. Minor refactoring of assign_backendlist_entry()

  17. Fix outdated comment; all running bgworkers are in BackendList

  18. Allow building with MSVC and Strawberry perl

  19. Fix rare failure in LDAP tests.

  20. Allow notifications to bgworkers without database connections.