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release-22.2: sql: fix left semi and left anti virtual lookup joins#92880

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yuzefovich merged 1 commit intocockroachdb:release-22.2from
yuzefovich:backport22.2-92713
Dec 3, 2022
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release-22.2: sql: fix left semi and left anti virtual lookup joins#92880
yuzefovich merged 1 commit intocockroachdb:release-22.2from
yuzefovich:backport22.2-92713

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@yuzefovich yuzefovich commented Dec 2, 2022

Backport 1/1 commits from #92713.

/cc @cockroachdb/release

This commit fixes the execution of the left semi and left anti virtual
lookup joins. The bug was that we forgot to project away the looked up
columns (coming from the "right" side) which could then lead to wrong
columns being used higher up the tree. The bug was introduced during
22.1 release cycle where we added the optimizer support for generating
plans that could contain left semi and left anti virtual lookup joins.
This commit fixes that issue as well as the output columns of such joins
(I'm not sure whether there is a user facing impact of having incorrect
"output columns").

Additionally, this commit fixes the execution of these virtual lookup
joins to correctly return the input row only once. Previously, for left
anti joins we'd be producing an output row if there was a match (which
is wrong), and for both left semi and left anti we would emit an output
row every time there was a match (but this should be done only once).
(Although I'm not sure whether it is possible for virtual indexes to
result in multiple looked up rows.)

Also, as a minor simplification this commit makes it so that the output
rows are not added into the row container for left semi and left anti
and the container is not instantiated at all.

Fixes: #91012.
Fixes: #88096.

Release note (bug fix): CockroachDB previously could incorrectly
evaluate queries that performed left semi and left anti "virtual lookup"
joins on tables in pg_catalog or information_schema. These join types
can be planned when a subquery is used inside of a filter condition. The
bug was introduced in 22.1.0 and is now fixed.

Release justification: bug fix.

@yuzefovich yuzefovich requested a review from msirek December 2, 2022 03:43
@yuzefovich yuzefovich requested a review from a team as a code owner December 2, 2022 03:43
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blathers-crl bot commented Dec 2, 2022 •
edited by yuzefovich
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Thanks for opening a backport.

Please check the backport criteria before merging:

  • Patches should only be created for serious issues or test-only changes.
  • Patches should not break backwards-compatibility.
  • Patches should change as little code as possible.
  • Patches should not change on-disk formats or node communication protocols.
  • Patches should not add new functionality.
  • Patches must not add, edit, or otherwise modify cluster versions; or add version gates.
If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.
  • There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
  • The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
  • New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
  • The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

  • What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
  • Will this work in a cluster of mixed patch versions? Did we test that?
  • If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

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cockroach-teamcity commented Dec 2, 2022

This change is Reviewable

rytaft
rytaft approved these changes Dec 2, 2022
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:lgtm: I added a couple of questions / suggestions for tests that you could consider adding in a follow-up PR (since this is a backport).

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: :shipit: complete! 1 of 0 LGTMs obtained (waiting on @msirek and @yuzefovich)

pkg/sql/virtual_table.go line 342 at r1 (raw file):

				return true, nil
			}
		case descpb.LeftSemiJoin:

Do you have any tests that exercise this case for semi join? (e.g., with your previous fix before the collab session, maybe a semi join would have returned multiple results?)

pkg/sql/logictest/testdata/logic_test/pg_catalog line 4693 at r1 (raw file):

	AND t.relname = 't91012'
	AND a.atttypid
		IN (SELECT oid FROM pg_type WHERE typname = ANY (ARRAY['int8']));

could we construct a similar case for anti join?

yuzefovich
yuzefovich commented Dec 2, 2022
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Thanks! I opened up #92937 and will squash it into the backports.

Reviewable status: :shipit: complete! 1 of 0 LGTMs obtained (waiting on @msirek and @rytaft)

pkg/sql/virtual_table.go line 342 at r1 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

Do you have any tests that exercise this case for semi join? (e.g., with your previous fix before the collab session, maybe a semi join would have returned multiple results?)

I doubt it. I spent some time trying to come up with cases where multiple matches are looked up in the virtual index but didn't succeed (the difficulty is that we have a few virtual indexes in general and most of them appear unique, then for those that aren't unique (like crdb_internal.jobs (status) and crdb_internal.cluster_database_privileges (database_name)) I couldn't come up with a query that would get left semi join).

pkg/sql/logictest/testdata/logic_test/pg_catalog line 4693 at r1 (raw file):

Previously, rytaft (Rebecca Taft) wrote…

could we construct a similar case for anti join?

Done in #92937.

rytaft
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Thanks!

Reviewable status: :shipit: complete! 1 of 0 LGTMs obtained (waiting on @msirek)

pkg/sql/virtual_table.go line 342 at r1 (raw file):

Previously, yuzefovich (Yahor Yuzefovich) wrote…

I doubt it. I spent some time trying to come up with cases where multiple matches are looked up in the virtual index but didn't succeed (the difficulty is that we have a few virtual indexes in general and most of them appear unique, then for those that aren't unique (like crdb_internal.jobs (status) and crdb_internal.cluster_database_privileges (database_name)) I couldn't come up with a query that would get left semi join).

Ok no worries

@yuzefovich
sql: fix left semi and left anti virtual lookup joins
878c29c 
This commit fixes the execution of the left semi and left anti virtual
lookup joins. The bug was that we forgot to project away the looked up
columns (coming from the "right" side) which could then lead to wrong
columns being used higher up the tree. The bug was introduced during
22.1 release cycle where we added the optimizer support for generating
plans that could contain left semi and left anti virtual lookup joins.
This commit fixes that issue as well as the output columns of such joins
(I'm not sure whether there is a user facing impact of having incorrect
"output columns").

Additionally, this commit fixes the execution of these virtual lookup
joins to correctly return the input row only once. Previously, for left
anti joins we'd be producing an output row if there was a match (which
is wrong), and for both left semi and left anti we would emit an output
row every time there was a match (but this should be done only once).
(Although I'm not sure whether it is possible for virtual indexes to
result in multiple looked up rows.)

Also, as a minor simplification this commit makes it so that the output
rows are not added into the row container for left semi and left anti
and the container is not instantiated at all.

Release note (bug fix): CockroachDB previously could incorrectly
evaluate queries that performed left semi and left anti "virtual lookup"
joins on tables in `pg_catalog` or `information_schema`. These join types
can be planned when a subquery is used inside of a filter condition. The
bug was introduced in 22.1.0 and is now fixed.
@yuzefovich yuzefovich merged commit b835389 into cockroachdb:release-22.2 Dec 3, 2022
@yuzefovich yuzefovich deleted the backport22.2-92713 branch December 3, 2022 22:17
@yuzefovich yuzefovich mentioned this pull request Dec 8, 2022
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