[store/tikv] support batch coprocessor for TiFlash (#16030) #16226
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cherry-pick #16030 to release-4.0
What problem does this PR solve?
Send batch coprocessor request which contains multiple regions to TiFlash Engine
Problem Summary:
What is changed and how it works?
What's Changed:
In old time, tidb sends requests to tiflash in the way of
per region per requests. But most queries that send to tiflash will involves massive regions, which have huge overhead. And tiflash cannot decide the concurrency of runtime by itself.How it Works:
coprocessor.BatchRequest.Related changes
we update kvproto pingcap/kvproto#586
####Side effects
We use a system variable tidb_allow_batch_cop to switch the batch cop mode. It has no effect on requests that send to tikv. For TiFlash, it only effects queries like 'Aggregation' and 'TopN' by default. In conclusion, its risk is very low.
**TPCH 50G Benchmark result **
Release note