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sql: add new tidb specific system variables #589
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lilin90
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yikeke:add-tidb-specific-system-variables
Sep 3, 2018
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Original file line number | Diff line number | Diff line change |
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@@ -116,6 +116,26 @@ set @@global.tidb_distsql_scan_concurrency = 10 | |
- This variable is used to set the concurrency of the `serial scan` operation. | ||
- Use a bigger value in OLAP scenarios, and a smaller value in OLTP scenarios. | ||
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### tidb_projection_concurrency | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: 4 | ||
- This variable is used to set the concurrency of the `Projection` operator. | ||
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### tidb_hashagg_partial_concurrency | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: 4 | ||
- This variable is used to set the concurrency of executing the concurrent `hash aggregation` algorithm in the `partial` phase. | ||
- When the parameter of the aggregate function is not distinct, HashAgg is run concurrently and respectively in two phases - the `partial` phase and the `final` phase. | ||
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### tidb_hashagg_final_concurrency | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: 4 | ||
- This variable is used to set the concurrency of executing the concurrent `hash aggregation` algorithm in the `final` phase. | ||
- When the parameter of the aggregate function is not distinct, HashAgg is run concurrently and respectively in two phases - the `partial` phase and the `final` phase. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. ditto |
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### tidb_index_join_batch_size | ||
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- Scope: SESSION | GLOBAL | ||
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@@ -237,6 +257,31 @@ set @@global.tidb_distsql_scan_concurrency = 10 | |
- Default: 0 | ||
- This variable is used to set whether to disable automatic retry of explicit transactions. If you set this variable to 1, the transaction does not retry automatically. If there is a conflict, the transaction needs to be retried at the application layer. To decide whether you need to disable automatic retry, see [description of optimistic transactions](transaction-isolation.md#description-of-optimistic-transactions). | ||
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## tidb_enable_table_partition | ||
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- Scope: SESSION | ||
- Default value: 0 | ||
- This variable is used to set whether to enable the `TABLE PARTITION` feature. | ||
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## tidb_backoff_lock_fast | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: 100 | ||
- This variable is used to set the `backoff` time when the read request meets a lock. | ||
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## tidb_ddl_reorg_worker_cnt | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: 16 | ||
- This variable is used to set the concurrency of the DDL operation in the `re-organize` phase. | ||
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## tidb_ddl_reorg_priority | ||
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- Scope: SESSION | GLOBAL | ||
- Default value: PRIORITY_NORMAL | ||
- This variable is used to set the priority of executing the `ADD INDEX` operation in the `re-organize` phase. | ||
- You can set the value of this variable to PRIORITY_LOW, PRIORITY_NORMAL or PRIORITY_HIGH. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. PRIORITY_LOW, PRIORITY_NORMAL or PRIORITY_HIGH -> |
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## Optimizer Hint | ||
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On the basis of MySQL’s `Optimizer Hint` Syntax, TiDB adds some proprietary `Hint` syntaxes. When using the `Hint` syntax, the TiDB optimizer will try to use the specific algorithm, which performs better than the default algorithm in some scenarios. | ||
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HashAgg ->
HashAgg