dm-best-practices: define N in the small-dataset DM-worker deployment guidance

[yahonda]

What is changed, added or deleted? (Required)

The deployment-plan table in dm/dm-best-practices.md recommends deploying "1~N DM-worker nodes according to the number of upstream data sources" without ever defining what N refers to. This PR rewords it to explicitly tie N to the number of upstream data sources: "Deploy 1 to N DM-worker nodes, where N is the number of upstream data sources."

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)

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

• This PR is translated from:
• Other reference link(s): fixes dm-best-practices.md: deployment table uses "1~N DM-worker nodes" without defining N #23744

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
  • Updated deployment guidance to clarify that DM workers should use between one and N nodes, where N matches the number of upstream data sources.

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📝 Walkthrough

Walkthrough

The deployment-plan table now states that DM-worker deployment uses 1 to N nodes, where N is the number of upstream data sources.

Changes

DM deployment guidance

Layer / File(s)	Summary
Clarify DM-worker node count dm/dm-best-practices.md	The deployment table defines N as the number of upstream data sources and uses “1 to N” DM-worker nodes.

Priority: ⬇️ Low — Impact reflects low issue severity.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to 85e6d

The deployment guidance now clearly defines N as the number of upstream data sources, removing ambiguity in the recommended DM-worker node range. No current merge-readiness risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the DM best-practices change and the definition of N in the DM-worker deployment guidance.
Description check	✅ Passed	The description explains the change, identifies the affected TiDB version, references issue #23744, records AI involvement, and completes the applicable checklist items. Optional fields are left blank…
Linked Issues check	✅ Passed	The change directly satisfies issue #23744 by defining N as the number of upstream data sources in the English DM best-practices deployment guidance for the release-8.5 branch.
Out of Scope Changes check	✅ Passed	The pull request changes only the deployment-plan wording in dm/dm-best-practices.md. The change is directly related to the linked issue and PR objective.
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…

✨ Finishing Touches

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