Update garbage collection docs

[morgo]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

This updates the docs for pingcap/tidb#21988 (now merged).

21988 still allows the previous methods for updating, but because these changes are not validated, they should not be recommended. Incorrect configuration can lead to strange behaviors.

Partially address #4549 (for backup page mentioned, there are still other pages that need readability improvements)

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

• master (the latest development version)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

• *: Move tikv gc configuration to sysvars tidb#21988

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

[TomShawn]

• Is this PR or will it be applicable to v5.0?
• Please involve technical reviews.

[MyonKeminta]

Can you keep the document for the old configuration way, but mark it to be unrecommended?

[morgo]

Can you keep the document for the old configuration way, but mark it to be unrecommended?

The old method does not validate the settings, so I think it should be discouraged. There is a note on garbage-collection-configuration.md which explains the old method:

In previous releases of TiDB, garbage collection was configured via the mysql.tidb table. While changes to this table continue to be supported, it is recommended to use the system variables provided.

I can change it to use a Note: so it is easier to spot.

[morgo]

• Is this PR or will it be applicable to v5.0?

My understanding is that the TiDB 5.0-rc branch is for the RC only, and 5.0 GA will be based on master. So yes, it will be in v5.0. I am not sure of the docs plan fo banching, since there is now a v5.0 branch. I am not sure how docs plans to handle this though.

• Please involve technical reviews.

Done.

[morgo]

/unlabel status/DNM

[ti-srebot]

@MyonKeminta, @youjiali1995, PTAL.

[ti-srebot]

@MyonKeminta, @youjiali1995, PTAL.

[MyonKeminta]

The modification to the document includes how to prevent GC to use tools safely. But I'm afraid currently those tools will block GC by setting service safepoints automatically, and the manual operations are only needed for old versions, where the variable syntax for GC configurations is not supported. @3pointer @kennytm PTAL, thanks

[morgo]

/unlabel status/require-change

[yikeke]

hi @overvenus if you agree with the tool part of this PR, can you leave a comment "/lgtm" to enable the bot to merge?

[overvenus]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• overvenus
• yikeke

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[yikeke]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 98f36fc

[ti-srebot]

cherry pick to release-5.0 in PR #5055

[qiancai]

/remove-translation doing

[qiancai]

/translation done