mysql (ticdc): Improve the performance of the mysql sink by refining the transaction event batching logic (#10466)

[ti-chi-bot]

This is an automated cherry-pick of #10466

What problem does this PR solve?

Issue Number: close #11241

What is changed and how it works?

1. When there are a lot of txns in worker's txnCh, we try to do flush until save batches to maxTxnRows, instead of doing flush with tiny txns because of ticker.C.
2. Adjust the calculation of worker-busy-ratio to make it more precise and more clear.
   The original calculation of worker-busy-ratio may have certain deviation when the flush time is long (such as larger than hundreds of milliseconds). And the longer the flush time, the larger the deviation. The reason for the deviation is that when the flsuh time is long, the interval between each time we increase the worker busy ratio value clearly exceeds 1s, resulting in the growth rate of the worker-busy-ratio per second being less than actual rate.

Performance Test Result

We take a large workload on upstream to keep worker-busy-ratio as 100%, and compare the improvement of sink performance before and after optimization.

1. Simulate network latency between the upstream and downstream is 2ms.
   After Optimization -- 33339 rows/s (+14%). Before Optimization -- 29075 rows/s
2. Simulate network latency between the upstream and downstream is 5ms.
   After Optimization -- 20528 rows/s(+13%). Before Optimization -- 18129 rows/s
3. Simulate network latency between the upstream and downstream is 20ms.
   After Optimization -- 7273 rows/s(+20%). Before Optimization -- 6048 rows/s
   

New panel of worker busy ratio

Check List

Tests

• Manual test (add detailed scripts or steps below)

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

None

[hongyunyan]

/retest

[ti-chi-bot]

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