br, cdc: remove cdclog sink and PiTR

[YuJuncen]

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)

According to @IANTHEREAL, the cdclog sink and the PiTR are just prototype features(even not experimental) and not ready to be documented. They should be removed for preventing misusing of them.

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

• master (the latest development version)
• v5.1 (TiDB 5.1 versions)
• 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)

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

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[YuJuncen]

/cc @3pointer, @IANTHEREAL

[YuJuncen]

/cc 3pointer
/cc IANTHEREAL

[dveeden]

I don't think removing the docs is the right step. If this is not production ready people should be warned about that.

Would be better to either:

• put a warning about this being very experimental and far from production ready into the docs
• put the feature behind a (compile time?) feature flag that is disabled for production builds
• remove the code and put it into a different branch or something similar
• Make the code production ready, maybe with a very reduced scope etc.

[IANTHEREAL]

It is always not easy to delete existing content. I have also tried to delete these content. The essence is that this feature is completely a prototype demo. It is irresponsible for any user to use or test

[IANTHEREAL]

I think we can move the code to another branch and delete it from the master branch. Then we can keep the document in a single document or delete them, how about it? @YuJuncen @dveeden

[dveeden]

@IANTHEREAL yes that sounds good to me

[kolbe]

I think we can move the code to another branch and delete it from the master branch. Then we can keep the document in a single document or delete them, how about it? @YuJuncen @dveeden

I'm glad to see that there's a plan to move the code elsewhere. It would be one thing if it were only in the master branch, but the fact it is also included in "GA" releases is really a very big problem.

[dveeden]

@IANTHEREAL @YuJuncen What is the plan with this PR?

[YuJuncen]

@dveeden @db-will has discussed with @IANTHEREAL, we decided to keep this document, marked them as 'experimental feature' (#6565).

Eh, BTW, if possible, please @IANTHEREAL take a look and make sure we can keep the document then. I will change the PR to fit the requirement of #6565 for now.

[dveeden]

The description of the PR and the diff don't seem to match.

Also note that the image on https://docs.pingcap.com/tidb/stable/ticdc-overview shows "Incremental backup". Should there be a note about this as well?

[dveeden]

@IANTHEREAL @3pointer can we make this ready to be merged?

[ti-chi-bot]

@YuJuncen: PR needs rebase.

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[dveeden]

@IANTHEREAL @3pointer @TomShawn Now that pingcap/tiflow#3599 is merged this should be removed isn't it?

[shichun-0415]

Fixed in #7500.