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planner: fix a panic during column pruning (#47883)#48811

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planner: fix a panic during column pruning (#47883)#48811
ti-chi-bot wants to merge 3 commits intopingcap:release-6.1from
ti-chi-bot:cherry-pick-47883-to-release-6.1

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This is an automated cherry-pick of #47883

What problem does this PR solve?

Issue Number: close #47331

Problem Summary:

What is changed and how it works?

Through my investigation, I identified several key points:

  1. The panic occurs during DeriveStats: p.StatsInfo().ColNDVs[selfSchema.Columns[i].UniqueID] = childProfile.RowCount.
  2. There's a discrepancy in the number of expressions and schema columns: the plan has 8 expressions but only 7 columns in the schema.
  3. The logic plan causing the panic is a projection (ID 25), generated by the joinReOrderSolver.
  4. Post-debugging, I noted that the schema undergoes changes after the LogicalProjection.PruneColumns process.
  5. On further debugging the PruneColumns function individually, I discovered that the schema of projection#25 is affected even before it's reached in the process.
  6. This led me to suspect a memory issue. Notably, projection#18 and projection#25 appear to share the same schema memory address (0x14006b557c0).
  7. Consequently, when a column is pruned from projection#18, projection#25 becomes corrupted, leading to a mismatch between expressions and columns.

So I cloned that schema and made sure we didn't have this kind of problem anymore.

Check List

Tests

  • Unit test
  • Integration test
  • Manual test (add detailed scripts or steps below)
  • No need to test
    • I checked and no code files have been changed.

Side effects

  • Performance regression: Consumes more CPU
  • Performance regression: Consumes more Memory
  • Breaking backward compatibility

Documentation

  • Affects user behaviors
  • Contains syntax changes
  • Contains variable changes
  • Contains experimental features
  • Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix a panic issue during column pruning

Signed-off-by: hi-rustin <rustin.liu@gmail.com>
Signed-off-by: hi-rustin <rustin.liu@gmail.com>
Signed-off-by: hi-rustin <rustin.liu@gmail.com>
@ti-chi-bot ti-chi-bot added release-note Denotes a PR that will be considered when it comes time to generate release notes. size/M Denotes a PR that changes 30-99 lines, ignoring generated files. type/cherry-pick-for-release-6.1 This PR is cherry-picked to release-6.1 from a source PR. labels Nov 22, 2023
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ti-chi-bot bot commented Nov 22, 2023

[APPROVALNOTIFIER] This PR is NOT APPROVED

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@ti-chi-bot ti-chi-bot added the cherry-pick-approved Cherry pick PR approved by release team. label Nov 23, 2023
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ti-chi-bot bot commented Feb 6, 2024

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

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idc-jenkins-ci-tidb/check_dev 7add326 link true /test check-dev
idc-jenkins-ci-tidb/unit-test 7add326 link true /test unit-test

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@0xPoe 0xPoe closed this Jul 31, 2024
@ti-chi-bot ti-chi-bot bot added do-not-merge/cherry-pick-not-approved and removed cherry-pick-approved Cherry pick PR approved by release team. labels Mar 4, 2025
@ti-chi-bot ti-chi-bot deleted the cherry-pick-47883-to-release-6.1 branch April 15, 2025 08:30
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