[WIP]: add v7.5.8 release notes

[doc-claw-bot]

What is changed, added or deleted? (Required)

• Add releases/release-7.5.8.md for the TiDB 7.5.8 patch release notes.
• This release-notes update is prepared on release-8.5 because the release-notes directory is maintained there and will be cherry-picked to master.

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s): generated from doc_4afdcdb19e49_release-7.5.8-updated-by-ai.md

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

Summary by CodeRabbit

• Documentation

  • Added TiDB 7.5.8 release notes covering improvements and fixes across TiDB, TiKV, PD, TiFlash, and TiCDC.

• Bug Fixes

  • Resolved crashes, statistics-loading panics, and excessive planner CPU usage.
  • Fixed stale safepoints, CDC connection issues, and Kafka resource leaks.
  • Addressed I/O-related throughput degradation and SST ingestion consistency.
  • Improved PD stability and TiFlash results involving null values.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Details

Needs approval from an approver in each of these files:

• OWNERS

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• releases/release-7.5.8.md

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📝 Walkthrough

Walkthrough

The release page adds TiDB 7.5.8 metadata, one PD improvement, and bug fixes across TiDB, TiKV, PD, TiFlash, and TiCDC.

Changes

TiDB 7.5.8 release notes

Layer / File(s)	Summary
Release metadata and PD improvement releases/release-7.5.8.md	Adds release information, quick-access links, and the store label for the pd_cluster_status metric.
Component bug fixes releases/release-7.5.8.md	Documents fixes for executor shutdowns, planner CPU usage, statistics loading, safepoints, CDC connections, ingestion, PD stability, TiFlash nullability results, and TiCDC Kafka resource leaks.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to fd560

This release-notes update documents TiDB 7.5.8 improvements and fixes without changing runtime behavior. No merge-readiness risk remains.

Suggested reviewers: qiancai

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the change, target versions, branch context, and reference file. It omits the AI agent involvement section and selects master and v8.5 instead of v7.5, which does not match th…	Add the AI agent involvement section from the template. Select v7.5 as the affected version, and select master or other branches only if the repository workflow requires those targets.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: adding TiDB 7.5.8 release notes. The [WIP] prefix is acceptable, although it is optional status information.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the change, target versions, branch context, and reference file. It omits the AI agent involvement section and selects master and v8.5 instead of v7.5, which does not match the TiDB 7.5.8 release notes described by the pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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• releases/release-7.5.8.md

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[lidezhu]

LGTM for CDC

[ti-chi-bot]

@lidezhu: adding LGTM is restricted to approvers and reviewers in OWNERS files.

Details

In response to this:

LGTM for CDC

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[windtalker]

lgtm

[ti-chi-bot]

@windtalker: adding LGTM is restricted to approvers and reviewers in OWNERS files.

Details

In response to this:

lgtm

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.

[JaySon-Huang]

Reuse the same release note that already released in v8.5.6

Suggested change

	- Fix the issue that TiFlash might return results inconsistent with TiKV after a column is modified from `NOT NULL` to `NULL` [#10680](https://github.com/pingcap/tiflash/issues/10680) @[JaySon-Huang](https://github.com/JaySon-Huang) <!-- component: storage --> <!-- pr: https://github.com/pingcap/tiflash/pull/10690 -->
	- Fix a potential data inconsistency issue between TiFlash and TiKV after executing a DDL statement to remove the `NOT NULL` constraint of a column [#10680](https://github.com/pingcap/tiflash/issues/10680) @[JaySon-Huang](https://github.com/JaySon-Huang) <!-- component: storage --> <!-- pr: https://github.com/pingcap/tiflash/pull/10690 -->