owner: Modified the update strategy of gcSafePoint (#1731)

[asddongmen]

What problem does this PR solve?

TiKV GC safe point will be blocked indefinitely due to TiCDC changefeed checkpoint stagnation.

What is changed and how it works?

Set a threshold Y: Regardless of the status of the changefeed, TiCDC is allowed to block TiKV GC safe time for Y hours at most.

The threshold Y is set in the config/config.go file as a variable named gc-TTL and the default value is 84000 seconds (24 hours).

Check List

Tests

• Unit test

• Manual test (add detailed scripts or steps below)
  step1: set defaultServerConfig.gcTTL = 20 in /pkg/config.go

step2: add log.Warn("try to update gcSafePoint", zap.Time("gcSafePoint", oracle.GetTimeFromTS(gcSafePoint))) below line 802 in cdc/owner.go to print log info

step3: In a shell window type tiup playground to deploy a tidb cluster.

step4: Move to ticdc directory, and type ./bin/cdc server to to start the cdc component。

step5: Type ./cdc cli changefeed create --pd=http://127.0.0.1:2379 --sink-uri="mysql://root@127.0.0.1:4000/" --changefeed-id="ttl-test-10" to create a changefeed.

step6: pause above changefeed, you would see gcSafePoint stop update:

step7: gcSafePoint update again after stop 20s:

Code changes

• Has exported function/method change

Side effects

• Possible performance regression

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release note

• Modified the update strategy of gcSafePoint. Fix the problem that TiKV GC safe point is blocked indefinitely due to TiCDC changefeed checkpoint stagnation.

[asddongmen]

/type cherry-pick-for-release-5.0

[zier-one]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• leoppro

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[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: dff895d

[amyangfei]

/run-kafka-tests

[amyangfei]

/run-integration-tests
/run-kafka-tests

[amyangfei]

/run-kafka-tests

[amyangfei]

/run-kafka-tests

[amyangfei]

/run-integration-tests
/run-kafka-tests

[ti-chi-bot]

@asddongmen: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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