Re: ResourceOwner refactoring

Hi,

I noticed that the patchset didn't make much progress since February
and decided to give it another round of code review.

> [...]. But in general, end-of-transaction activities should be kept
> simple, especially between the release phases, so I feel that having to
> remember extra resources there is a bad code smell and we shouldn't
> encourage that.

+1

> I added a test module in src/test/modules/test_resowner to test those cases.

This is much appreciated, as well as extensive changes made to READMEs
and the comments.

> [...] New patchset attached.
> I added it as a separate patch on top of the previous patches, as
> v13-0003-Release-resources-in-
> priority-order.patch, to make it easier to
> see what changed after the previous patchset version. But it should be
> squashed with patch 0002 before committing.

My examination, which besides reading the code included running it
under sanitizer and checking the code coverage, didn't reveal any
major problems with the patchset.

Certain "should never happen in practice" scenarios seem not to be
test-covered in resowner.c, particularly:

```
elog(ERROR, "ResourceOwnerEnlarge called after release started");
elog(ERROR, "ResourceOwnerRemember called but array was full");
elog(ERROR, "ResourceOwnerForget called for %s after release started",
kind->name);
elog(ERROR, "%s %p is not owned by resource owner %s",
elog(ERROR, "ResourceOwnerForget called for %s after release started",
kind->name);
elog(ERROR, "lock reference %p is not owned by resource owner %s"
```

I didn't check whether these or similar code paths were tested before
the patch and I don't have a strong opinion on whether we should test
these scenarios. Personally I'm OK with the fact that these few lines
are not covered with tests.

The following procedures are never executed:

* RegisterResourceReleaseCallback()
* UnregisterResourceReleaseCallback()

And are never actually called anymore due to changes in 0005.
Previously they were used by contrib/pgcrypto. I suggest dropping this
part of the API since it seems to be redundant now. This will simplify
the implementation even further.

This patch, although moderately complicated, was moved between several
commitfests. I think it would be great if it made it to PG16. I'm
inclined to change the status of the patchset to RfC in a bit, unless
anyone has a second opinion.

--
Best regards,
Aleksander Alekseev