sessionctx/variable: refine TiDB specific system variables. #2915
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Added index lookup size and index lookup concurrency global variable. Organized TiDB specific system variables and added documentation.
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CI failed. @coocood |
| for total > 0 { | ||
| if batchSize > total { | ||
| batchSize = total | ||
| } | ||
| taskSizes = append(taskSizes, batchSize) | ||
| total -= batchSize | ||
| if batchSize < MaxLookupTableTaskSize { |
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why change the old strategy ?
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The old strategy doesn't work well.
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LGTM |
| @@ -254,7 +254,7 @@ func upgrade(s Session) { | |||
| func upgradeToVer2(s Session) { | |||
| // Version 2 add two system variable for DistSQL concurrency controlling. | |||
| // Insert distsql related system variable. | |||
| distSQLVars := []string{variable.DistSQLScanConcurrencyVar, variable.DistSQLJoinConcurrencyVar} | |||
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Why remove DistSQLJoinConcurrencyVar?
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It's not used right now, we can easily add it later if needed.
We add it before hand because we used need to update bootstrap version for adding new global variable.
| {ScopeGlobal | ScopeSession, TiDBDistSQLScanConcurrency, strconv.Itoa(DefDistSQLScanConcurrency)}, | ||
| {ScopeGlobal | ScopeSession, TiDBIndexLookupSize, strconv.Itoa(DefIndexLookupSize)}, | ||
| {ScopeGlobal | ScopeSession, TiDBIndexLookupConcurrency, strconv.Itoa(DefIndexLookupConcurrency)}, | ||
| {ScopeGlobal | ScopeSession, TiDBSkipDDLWait, boolToIntStr(DefSkipDDLWait)}, |
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TiDBSkipDDLWait should be session scope only. It is not safe to make it global scope.
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Third-party benchmark and loading tools create a lot of tables in a single TiDB server, we can't set session variables for them.
Make it a global variable is the only way.
We have well documented the risk to use this variable.
I think users can have the option.
Added index lookup size and index lookup concurrency global variable.
Organized TiDB specific system variables and added documentation.