docs: clarify how to disable TiFlash MPP after v7.3

[doc-claw-bot]

What is changed, added or deleted? (Required)

Clarify the instructions for disabling TiFlash MPP in explore-htap.md and tiflash/use-tiflash-mpp-mode.md.

For TiDB v7.3.0 and later, if users disable tidb_allow_mpp but still want TiFlash to execute queries, they also need to enable tidb_allow_tiflash_cop. Otherwise, queries might return errors.

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• 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)

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

• This PR is translated from:
• Other reference link(s):
  • https://github.com/pingcap/docs/blob/release-8.5/system-variables.md#tidb_allow_mpp-new-in-v50
  • https://github.com/pingcap/tidb/blob/master/pkg/executor/test/tiflashtest/tiflash_test.go#L1227-L1261

AI agent involvement

• The changes in this PR were primarily made by an AI agent on behalf of the PR author.

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
  • Clarified TiFlash settings for running queries without MPP on TiDB v7.3.0 and later: enable tidb_allow_tiflash_cop to use Cop or BatchCop, or set tidb_allow_mpp=0 alone when TiFlash should not execute queries.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The documentation clarifies how to disable MPP while retaining TiFlash Cop or BatchCop execution on TiDB v7.3.0 and later. It also distinguishes this from disabling TiFlash query execution.

Changes

TiFlash MPP guidance

Layer / File(s)	Summary
Document TiFlash execution settings explore-htap.md, tiflash/use-tiflash-mpp-mode.md	For TiDB v7.3.0 and later, the guidance sets tidb_allow_tiflash_cop=1 with tidb_allow_mpp=0 for non-MPP TiFlash execution. It clarifies that tidb_allow_mpp=0 alone is sufficient when TiFlash should not execute queries.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Merge Risk: 🔵 Low · up to 8b3a7

Operators may leave TiFlash execution enabled while believing MPP-off disables it. This is a bounded documentation issue with a straightforward correction.

Architecture Summary

Architecture risk: 🔵 Low · up to 8b3a7

The change affects 2 systems.

Changed systems: explore-htap.md, tiflash

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — explore-htap.md (service) was modified; 1 changed file maps to changed impact.
• observed — tiflash (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in explore-htap.md: The MPP-disable instructions now specify that TiDB v7.3.0 or later also requires tidb_allow_tiflash_cop to be ON for non-MPP Cop or BatchCop execution; otherwise, queries might return errors.
• observed — Modified behavior in tiflash/use-tiflash-mpp-mode.md: The example now applies to TiDB v7.3.0 and later and sets tidb_allow_tiflash_cop=1 alongside tidb_allow_mpp=0, allowing TiFlash query execution without MPP. It also states that setting only tidb_allow_mpp=0 suffices when TiFlash should not execute queries; the previous example set only that variable and did not distinguish the two outcomes.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main documentation change: clarifying how to disable TiFlash MPP for TiDB versions after v7.3.
Description check	✅ Passed	The description explains what changed, why it changed, the affected TiDB versions, reference links, AI involvement, and applicable change categories. The required sections are substantially complete.
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.

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[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Repository: pingcap/docs/.coderabbit.yaml
• Review profile: ASSERTIVE
• Plan: Advanced
• Run ID: c1a9ede3-eada-4e60-9103-df4d59d022a5

📥 Commits

Reviewing files that changed from the base of the PR and between 49ed15d and 8b3a7e6.

📒 Files selected for processing (2)

• explore-htap.md
• tiflash/use-tiflash-mpp-mode.md

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 2 remain after this review.

[coderabbitai]

🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Clarify the tidb_allow_mpp=0 requirement.

When tidb_allow_tiflash_cop=ON, disabling MPP still permits Cop and BatchCop plan selection.

If you want to prevent TiFlash from executing queries after disabling the MPP mode, also set `tidb_allow_tiflash_cop=OFF`. If `tidb_allow_tiflash_cop` remains at its default value of `OFF`, setting only `tidb_allow_mpp=0` prevents TiFlash execution.

🧰 Tools

🪛 GitHub Check: vale

[warning] 46-46:
[vale] reported by reviewdog 🐶
[PingCAP.Ambiguous] Consider using a clearer word than 'sufficient' because it may cause confusion.

Raw Output:
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