ddl: do not fill TiKV block cache for reorg coprocessor scans

[sanketkedia]

What problem does this PR solve?

Issue Number: close #69875

Problem Summary:

Reorg coprocessor scans are single-pass bulk reads over the whole table/index
range. They are sent with NotFillCache = false, so every scanned block is
inserted into the TiKV block cache. Those blocks are never re-read by the reorg,
so caching them brings no benefit while risking eviction of the working set that
concurrent foreground traffic relies on — regressing foreground read
latency during an online ADD INDEX on a large table.

What changed and how does it work?

Set NotFillCache = true on the shared reorg DistSQLContext
(newDefaultReorgDistSQLCtx). All reorg coprocessor scans are built from this
context (via SetFromSessionVars), so they now skip filling the block cache.

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

Reduce TiKV block cache pollution during DDL reorg (e.g. `ADD INDEX`) by not filling the block cache for reorg coprocessor scans.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign tiancaiamao for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• pkg/ddl/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

Hi @sanketkedia. Thanks for your PR.

I'm waiting for a pingcap member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[coderabbitai]

Caution

Review failed

An error occurred during the review process. Please try again later.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="Running error: context loading failed: failed to load packages: failed to load packages: failed to load with go/packages: context deadline exceeded"
level=error msg="Timeout exceeded: try increasing it by passing --timeout option"

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[joechenrh]

/ok-to-test

[ti-chi-bot]

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

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	ace2eed	link	true	/test check-dev2
pull-integration-realcluster-test-next-gen	ace2eed	link	true	/test pull-integration-realcluster-test-next-gen

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.6140%. Comparing base (531e40c) to head (ace2eed).

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #69876        +/-   ##
================================================
- Coverage   76.3207%   75.6140%   -0.7067%     
================================================
  Files          2041       2084        +43     
  Lines        559975     582365     +22390     
================================================
+ Hits         427377     440350     +12973     
- Misses       131697     139884      +8187     
- Partials        901       2131      +1230     

Flag	Coverage Δ
integration	45.6804% <100.0000%> (+5.9751%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	60.4471% <ø> (ø)
parser	∅ <ø> (∅)
br	63.9686% <ø> (+1.2473%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.