Обсуждение: Test to dump and restore objects left behind by regression

Hi All,
In [1] we found that having a test to dump and restore objects left
behind by regression test is missing. Such a test would cover many
dump restore scenarios without much effort. It will also help identity
problems described in the same thread [2] during development itself.

I am starting a new thread to discuss such a test. Attached is a WIP
version of the test. The test does fail at the restore step when
commit 74563f6b90216180fc13649725179fc119dddeb5 is reverted
reintroducing the problem.

Attached WIP test is inspired from
src/bin/pg_upgrade/t/002_pg_upgrade.pl which tests binary-upgrade
dumps. Attached test tests the non-binary-upgrade dumps.

Similar to 0002_pg_upgrade.pl the test uses SQL dumps before and after
dump and restore to make sure that the objects are restored correctly.
The test has some shortcomings
1. Objects which are not dumped at all are never tested.
2. Since the rows are dumped in varying order by the two clusters, the
test only tests schema dump and restore.
3. The order of columns of the inheritance child table differs
depending upon the DDLs used to reach a given state. This introduces
diffs in the SQL dumps before and after restore. The test ignores
these diffs by hardcoding the diff in the test.

Even with 1 and 2 the test is useful to detect dump/restore anomalies.
I think we should improve 3, but I don't have a good and simpler
solution. I didn't find any way to compare two given clusters in our
TAP test framework. Building it will be a lot of work. Not sure if
it's worth it.

Suggestions welcome.

[1] https://www.postgresql.org/message-id/CAExHW5vyqv%3DXLTcNMzCNccOrHiun_XhYPjcRqeV6dLvZSamriQ%40mail.gmail.com
[2] https://www.postgresql.org/message-id/3462358.1708107856%40sss.pgh.pa.us

--
Best Wishes,
Ashutosh Bapat

On Wed, Feb 21, 2024 at 12:18:45PM +0530, Ashutosh Bapat wrote:
> Even with 1 and 2 the test is useful to detect dump/restore anomalies.
> I think we should improve 3, but I don't have a good and simpler
> solution. I didn't find any way to compare two given clusters in our
> TAP test framework. Building it will be a lot of work. Not sure if
> it's worth it.

+    my $rc =
+      system($ENV{PG_REGRESS}
+          . " $extra_opts "
+          . "--dlpath=\"$dlpath\" "
+          . "--bindir= "
+          . "--host="
+          . $node->host . " "
+          . "--port="
+          . $node->port . " "
+          . "--schedule=$srcdir/src/test/regress/parallel_schedule "
+          . "--max-concurrent-tests=20 "
+          . "--inputdir=\"$inputdir\" "
+          . "--outputdir=\"$outputdir\"");

I am not sure that it is a good idea to add a full regression test
cycle while we have already 027_stream_regress.pl that would be enough
to test some dump scenarios.  These are very expensive and easy to
notice even with a high level of parallelization of the tests.
--
Michael

On Thu, Feb 22, 2024 at 6:32 AM Michael Paquier <michael@paquier.xyz> wrote:
>
> On Wed, Feb 21, 2024 at 12:18:45PM +0530, Ashutosh Bapat wrote:
> > Even with 1 and 2 the test is useful to detect dump/restore anomalies.
> > I think we should improve 3, but I don't have a good and simpler
> > solution. I didn't find any way to compare two given clusters in our
> > TAP test framework. Building it will be a lot of work. Not sure if
> > it's worth it.
>
> +       my $rc =
> +         system($ENV{PG_REGRESS}
> +                 . " $extra_opts "
> +                 . "--dlpath=\"$dlpath\" "
> +                 . "--bindir= "
> +                 . "--host="
> +                 . $node->host . " "
> +                 . "--port="
> +                 . $node->port . " "
> +                 . "--schedule=$srcdir/src/test/regress/parallel_schedule "
> +                 . "--max-concurrent-tests=20 "
> +                 . "--inputdir=\"$inputdir\" "
> +                 . "--outputdir=\"$outputdir\"");
>
> I am not sure that it is a good idea to add a full regression test
> cycle while we have already 027_stream_regress.pl that would be enough
> to test some dump scenarios.

That test *uses* pg_dump as a way to test whether the two clusters are
in sync. The test might change in future to use some other method to
make sure the two clusters are consistent. Adding the test here to
that test will make that change much harder.

It's not the dump, but restore, we are interested in here. No test
that runs PG_REGRESS also runs pg_restore in non-binary mode.

Also we need to keep this test near other pg_dump tests, not far from them.

> These are very expensive and easy to
> notice even with a high level of parallelization of the tests.

I agree, but I didn't find a suitable test to ride on.

--
Best Wishes,
Ashutosh Bapat

On 22.02.24 02:01, Michael Paquier wrote:
> On Wed, Feb 21, 2024 at 12:18:45PM +0530, Ashutosh Bapat wrote:
>> Even with 1 and 2 the test is useful to detect dump/restore anomalies.
>> I think we should improve 3, but I don't have a good and simpler
>> solution. I didn't find any way to compare two given clusters in our
>> TAP test framework. Building it will be a lot of work. Not sure if
>> it's worth it.
> 
> +    my $rc =
> +      system($ENV{PG_REGRESS}
> +          . " $extra_opts "
> +          . "--dlpath=\"$dlpath\" "
> +          . "--bindir= "
> +          . "--host="
> +          . $node->host . " "
> +          . "--port="
> +          . $node->port . " "
> +          . "--schedule=$srcdir/src/test/regress/parallel_schedule "
> +          . "--max-concurrent-tests=20 "
> +          . "--inputdir=\"$inputdir\" "
> +          . "--outputdir=\"$outputdir\"");
> 
> I am not sure that it is a good idea to add a full regression test
> cycle while we have already 027_stream_regress.pl that would be enough
> to test some dump scenarios.  These are very expensive and easy to
> notice even with a high level of parallelization of the tests.

The problem is, we don't really have any end-to-end coverage of

dump
restore
dump again
compare the two dumps

with a database with lots of interesting objects in it.

Note that each of these steps could fail.

We have somewhat relied on the pg_upgrade test to provide this testing, 
but we have recently discovered that the dumps in binary-upgrade mode 
are different enough to not test the normal dumps well.

Yes, this test is a bit expensive.  We could save some time by doing the 
first dump at the end of the normal regress test and have the pg_dump 
test reuse that, but then that would make the regress test run a bit 
longer.  Is that a better tradeoff?

I have done some timing tests:

master:

pg_dump check:     22s
pg_dump check -j8: 8s
check-world -j8:   2min44s

patched:

pg_dump check:     34s
pg_dump check -j8: 13s
check-world -j8:   2min46s

So overall it doesn't seem that bad.

> On 22 Feb 2024, at 10:16, Peter Eisentraut <peter@eisentraut.org> wrote:

> We have somewhat relied on the pg_upgrade test to provide this testing, but we have recently discovered that the
dumpsin binary-upgrade mode are different enough to not test the normal dumps well. 
>
> Yes, this test is a bit expensive.  We could save some time by doing the first dump at the end of the normal regress
testand have the pg_dump test reuse that, but then that would make the regress test run a bit longer.  Is that a better
tradeoff?

Something this expensive seems like what PG_TEST_EXTRA is intended for, we
already have important test suites there.

But.  We know that the cluster has an interesting state when the pg_upgrade
test starts, could we use that to make a dump/restore test before continuing
with testing pg_upgrade?  It can be argued that pg_upgrade shouldn't be
responsible for testing pg_dump, but it's already now a pretty important
testcase for pg_dump in binary upgrade mode so it's that far off.  If pg_dump
has bugs then pg_upgrade risks subtly breaking.

When upgrading to the same version, we could perhaps also use this to test a
scenario like: Dump A, restore into B, upgrade B into C, dump C and compare C
to A.

--
Daniel Gustafsson

On Thu, Feb 22, 2024 at 3:03 PM Daniel Gustafsson <daniel@yesql.se> wrote:
>
> > On 22 Feb 2024, at 10:16, Peter Eisentraut <peter@eisentraut.org> wrote:
>
> > We have somewhat relied on the pg_upgrade test to provide this testing, but we have recently discovered that the
dumpsin binary-upgrade mode are different enough to not test the normal dumps well. 
> >
> > Yes, this test is a bit expensive.  We could save some time by doing the first dump at the end of the normal
regresstest and have the pg_dump test reuse that, but then that would make the regress test run a bit longer.  Is that
abetter tradeoff? 
>
> Something this expensive seems like what PG_TEST_EXTRA is intended for, we
> already have important test suites there.

That's ok with me.

>
> But.  We know that the cluster has an interesting state when the pg_upgrade
> test starts, could we use that to make a dump/restore test before continuing
> with testing pg_upgrade?  It can be argued that pg_upgrade shouldn't be
> responsible for testing pg_dump, but it's already now a pretty important
> testcase for pg_dump in binary upgrade mode so it's that far off.  If pg_dump
> has bugs then pg_upgrade risks subtly breaking.

Somebody looking for dump/restore tests wouldn't search
src/bin/pg_upgrade, I think. However if more people think we should
just add this test 002_pg_upgrade.pl, I am fine with it.

>
> When upgrading to the same version, we could perhaps also use this to test a
> scenario like: Dump A, restore into B, upgrade B into C, dump C and compare C
> to A.

If comparison of C to A fails, we wouldn't know which step fails. I
would rather compare outputs of each step separately.

--
Best Wishes,
Ashutosh Bapat

> On 22 Feb 2024, at 10:55, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> wrote:
> On Thu, Feb 22, 2024 at 3:03 PM Daniel Gustafsson <daniel@yesql.se> wrote:

> Somebody looking for dump/restore tests wouldn't search
> src/bin/pg_upgrade, I think.

Quite possibly not, but pg_upgrade is already today an important testsuite for
testing pg_dump in binary-upgrade mode so maybe more developers touching
pg_dump should?

>> When upgrading to the same version, we could perhaps also use this to test a
>> scenario like: Dump A, restore into B, upgrade B into C, dump C and compare C
>> to A.
>
> If comparison of C to A fails, we wouldn't know which step fails. I
> would rather compare outputs of each step separately.

To be clear, this wasn't intended to replace what you are proposing, but an
idea for using it to test *more* scenarios.

--
Daniel Gustafsson

On 22.02.24 11:00, Daniel Gustafsson wrote:
>> On 22 Feb 2024, at 10:55, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> wrote:
>> On Thu, Feb 22, 2024 at 3:03 PM Daniel Gustafsson <daniel@yesql.se> wrote:
> 
>> Somebody looking for dump/restore tests wouldn't search
>> src/bin/pg_upgrade, I think.
> 
> Quite possibly not, but pg_upgrade is already today an important testsuite for
> testing pg_dump in binary-upgrade mode so maybe more developers touching
> pg_dump should?

Yeah, I think attaching this to the existing pg_upgrade test would be a 
good idea.  Not only would it save test run time, it would probably also 
reduce code duplication.

Peter Eisentraut <peter@eisentraut.org> writes:
> The problem is, we don't really have any end-to-end coverage of

> dump
> restore
> dump again
> compare the two dumps

> with a database with lots of interesting objects in it.

I'm very much against adding another full run of the core regression
tests to support this.  But beyond the problem of not bloating the
check-world test runtime, there is the question of what this would
actually buy us.  I doubt that it is worth very much, because
it would not detect bugs-of-omission in pg_dump.  As I remarked in
the other thread, if pg_dump is blind to the existence of some
feature or field, testing that the dumps compare equal will fail
to reveal that it didn't restore that property.

I'm not sure what we could do about that.  One could imagine writing
some test infrastructure that dumps out the contents of the system
catalogs directly, and comparing that instead of pg_dump output.
But that'd be a lot of infrastructure to write and maintain ...
and it's not real clear why it wouldn't *also* suffer from
I-forgot-to-add-this hazards.

On balance, I think there are good reasons that we've not added
such a test, and I don't believe those tradeoffs have changed.

            regards, tom lane

On Thu, Feb 22, 2024 at 3:50 PM Peter Eisentraut <peter@eisentraut.org> wrote:
>
> On 22.02.24 11:00, Daniel Gustafsson wrote:
> >> On 22 Feb 2024, at 10:55, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> wrote:
> >> On Thu, Feb 22, 2024 at 3:03 PM Daniel Gustafsson <daniel@yesql.se> wrote:
> >
> >> Somebody looking for dump/restore tests wouldn't search
> >> src/bin/pg_upgrade, I think.
> >
> > Quite possibly not, but pg_upgrade is already today an important testsuite for
> > testing pg_dump in binary-upgrade mode so maybe more developers touching
> > pg_dump should?
>
> Yeah, I think attaching this to the existing pg_upgrade test would be a
> good idea.  Not only would it save test run time, it would probably also
> reduce code duplication.
>

That's more than one vote for adding the test to 002_pg_ugprade.pl.
Seems fine to me.

--
Best Wishes,
Ashutosh Bapat

On Thu, Feb 22, 2024 at 8:35 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Peter Eisentraut <peter@eisentraut.org> writes:
> > The problem is, we don't really have any end-to-end coverage of
>
> > dump
> > restore
> > dump again
> > compare the two dumps
>
> > with a database with lots of interesting objects in it.
>
> I'm very much against adding another full run of the core regression
> tests to support this.

This will be taken care of by Peter's latest idea of augmenting
existing 002_pg_upgrade.pl.

> But beyond the problem of not bloating the
> check-world test runtime, there is the question of what this would
> actually buy us.  I doubt that it is worth very much, because
> it would not detect bugs-of-omission in pg_dump.  As I remarked in
> the other thread, if pg_dump is blind to the existence of some
> feature or field, testing that the dumps compare equal will fail
> to reveal that it didn't restore that property.
>
> I'm not sure what we could do about that.  One could imagine writing
> some test infrastructure that dumps out the contents of the system
> catalogs directly, and comparing that instead of pg_dump output.
> But that'd be a lot of infrastructure to write and maintain ...
> and it's not real clear why it wouldn't *also* suffer from
> I-forgot-to-add-this hazards.

If a developer forgets to add logic to dump objects that their patch
adds, it's hard to detect it, through testing alone, in every possible
case. We need reviewers to take care of that. I don't think that's the
objective of this test case or of pg_upgrade test either.

>
> On balance, I think there are good reasons that we've not added
> such a test, and I don't believe those tradeoffs have changed.
>

I am not aware of those reasons. Are they documented somewhere? Any
pointers to the previous discussion on this topic? Googling "pg_dump
regression pgsql-hackers" returns threads about performance
regressions.

On the flip side, the test I wrote reproduces the COMPRESSION/STORAGE
bug you reported along with a few other bugs in that area which I will
report soon on that thread. I think, that shows that we need such a
test.

--
Best Wishes,
Ashutosh Bapat