Make index serial scan concurrency configurable and fix golint errors. #2928
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coocood
reviewed
Mar 26, 2017
sessionctx/variable/tidb_vars.go
Outdated
| @@ -70,6 +70,10 @@ const ( | |||
| // Set this value higher may reduce the latency but consumes more system resource. | |||
| TiDBIndexLookupConcurrency = "tidb_index_lookup_concurrency" | |||
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| // tidb_index_serial_scan_concurrency is user for controling the concurrency of index scan operation | |||
shenli
changed the title
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Hi, do we have any bench results ? |
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LGTM |
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@ngaut In one of SMJ case, I increase the concurrency from 1 to 3 and query time drop from 2min to 1min 30sec. But this will cost more memory. |
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Cool |
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When doing index double read operation with keepOrder as true, we use only one worker. If we need to read a lot of data, it will be quite slow. So I make it configurable. For OLAP TiDB cluster, we could set the concurrency to 4 or 5.
I will add test in the next commit.