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Query Cache: Try to fix bad cast from ColumnConst to ColumnVector<char8_t>#50704

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rschu1ze:qc-materialize-query
Jun 23, 2023
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Query Cache: Try to fix bad cast from ColumnConst to ColumnVector<char8_t>#50704
alexey-milovidov merged 2 commits intoClickHouse:masterfrom
rschu1ze:qc-materialize-query

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@rschu1ze rschu1ze commented Jun 8, 2023 •
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Hopefully resolves #49445

The query cache buffers query result chunks and eventually squashes them before insertion into the cache. Here, squashing failed because not all chunks were of the same type. Looks like chunks of the same underlying type (e.g. UInt8) in a query result can be of mixed const, sparse or low-cardinality type. Fixed this by always materializing the data regardless of the compression. Strange thing is that the failing query in the stress test (*) isn't able to reproduce the bug, and I haven't managed to trigger the issue otherwise --> no test case added.

(*) SELECT 1 UNION ALL SELECT 1 INTERSECT SELECT 1, here

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  • Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Fix assert in query cache with mixed const/non-const result chunks

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robot-clickhouse-ci-2 commented Jun 8, 2023 •
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This is an automated comment for commit a9f1393 with description of existing statuses. It's updated for the latest CI running
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The overall status of the commit is 🔴 error

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@robot-clickhouse-ci-2 robot-clickhouse-ci-2 added the pr-bugfix Pull request with bugfix, not backported by default label Jun 8, 2023
@alexey-milovidov alexey-milovidov added the pr-must-backport Pull request should be backported intentionally. Use this label with great care! label Jun 10, 2023
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alexey-milovidov commented Jun 10, 2023

LGTM, but the tests have failed. Please fix the tests first.

Also,

Bugfix validate check | Checks that either a new test (functional or integration) or there some changed tests that fail with the binary built on master branch

please add a new test.

@alexey-milovidov alexey-milovidov self-assigned this Jun 10, 2023
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alexey-milovidov commented Jun 20, 2023

@rschu1ze add a test plz.

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alexey-milovidov commented Jun 21, 2023

Please add a test.

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rschu1ze commented Jun 21, 2023

Sorry, this PR got a bit rusty. Checking again locally now, in my first try two weeks ago I could not find a repro.

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alexey-milovidov commented Jun 21, 2023

It's ok to add a test that could only occasionally reproduce the issue.

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rschu1ze commented Jun 22, 2023

Update: As the original issue happened (sporadically) during stress testing, I isolated the bad query + test case, and ran it with query cache enabled + custom settings from the stress test overnight in a loop. Didn't reproduce and no other repro exists right now 😞

There were a few new issues in CI:

  • bad_cast in other (non-query-cache) locations during stress testing. All of them are about casts to ColumnLowCardinality (the original issue was a bad cast from ColumnConst). Could be related but not sure. I'll try to make the fix more minimal for now.
  • the upgrade check in stress test failed ("Cached disk is allowed only on top of object storage. (BAD_ARGUMENTS)"). I think this is unrelated.

rschu1ze added 2 commits June 22, 2023 11:46
@rschu1ze
Query Cache: Try to fix bad cast from ColumnConst to ColumnVector<cha…
a1c131c 
…r8_t>

Resolves ClickHouse#49445

The query cache buffers query result chunks and eventually squashes
them before insertion into the cache. Here, squashing failed because not
all chunks were of the same type. Looks like chunks of the same
underlying type (e.g. UInt8) in a query result be of mixed const, sparse
or low-cardinality type. Fix this by always materializing the data
regardless of the compression. Strange thing is that the failing query
in the stress test (*) isn't able to reproduce the bug, and I haven't
managed to trigger the issue otherwise, so no test case is added.

(*) SELECT 1 UNION ALL SELECT 1 INTERSECT SELECT 1
    E.g. here: https://s3.amazonaws.com/clickhouse-test-reports/0/18817517ed6f8849e3d979e10fbb273e0edf0eaa/stress_test__debug_/fatal_messages.txt
@rschu1ze
Make the fix more minimal
a9f1393
@rschu1ze rschu1ze force-pushed the qc-materialize-query branch from 4daba82 to a9f1393 Compare June 22, 2023 11:46
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rschu1ze commented Jun 23, 2023

ClickHouse Integration Tests (asan) [4/6]:

ClickHouse Stateless Tests (release, Wide Parts Enabled):

ClickHouse Bugfix Validate Check for PR:

  • ... well, no repro exists but I am pretty sure that the PR fixes the issue.

@alexey-milovidov alexey-milovidov merged commit 305e3d1 into ClickHouse:master Jun 23, 2023
This was referenced Jun 23, 2023
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@robot-ch-test-poll1 robot-ch-test-poll1 mentioned this pull request Jun 23, 2023
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robot-clickhouse added a commit that referenced this pull request Jun 23, 2023
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Backport #50704 to 23.5: Query Cache: Try to fix bad cast from Column…
49ff77b 
…Const to ColumnVector<char8_t>
@robot-clickhouse-ci-2 robot-clickhouse-ci-2 added the pr-backports-created Backport PRs are successfully created, it won't be processed by CI script anymore label Jun 23, 2023
alexey-milovidov added a commit that referenced this pull request Jun 24, 2023
@alexey-milovidov
Merge pull request #51334 from ClickHouse/backport/23.5/50704
2e4b52a 
Backport #50704 to 23.5: Query Cache: Try to fix bad cast from ColumnConst to ColumnVector<char8_t>
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Bad cast from type DB::ColumnConst to DB::ColumnVector<char8_t>

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