[store/tikv] support batch coprocessor for TiFlash #16030
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ghost
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lzmhhh123
reviewed
Apr 7, 2020
wshwsh12
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Apr 7, 2020
Codecov Report
@@ Coverage Diff @@
## master #16030 +/- ##
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Coverage 80.5758% 80.5758%
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Files 506 506
Lines 137077 137077
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Hits 110451 110451
Misses 18133 18133
Partials 8493 8493 |
lzmhhh123
reviewed
Apr 8, 2020
lzmhhh123
reviewed
Apr 8, 2020
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| func (c *CopClient) sendBatch(ctx context.Context, req *kv.Request, vars *kv.Variables) kv.Response { | ||
| if req.KeepOrder || req.Desc { | ||
| return copErrorResponse{errors.New("batch coprocessor cannot prove keep order or desc property")} |
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Since TiFlash can keep order for handle scan. When we enable the batch cop request, there is none guarantee to keep order for the handle column. So we should ban the order properties' satisfaction in the planner.
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It's not easy to consider allow_batch in planner. For safe and convient, I will check KeepOrder in executor/builder.go, If it is true, batch_cop is forced to set flase.
This part of code is remained as proctection.
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OK, that's also another solution.
lzmhhh123
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Apr 8, 2020
lzmhhh123
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status/can-merge
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/run-all-tests |
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cherry pick to release-4.0 in PR #16226 |
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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