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add distinct-agg-push-down in tidb config file (#3259) #3266

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Jul 14, 2020
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add distinct-agg-push-down in tidb config file (#3259) #3266

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fa5eabf
cherry pick #3259 to release-4.0
ran-huang Jul 14, 2020
42dd463
resolve conflict
ran-huang Jul 14, 2020
6fc7f8e
resolve conflict
ran-huang Jul 14, 2020
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3 changes: 1 addition & 2 deletions system-variables.md
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Original file line number Diff line number Diff line change
@@ -1,8 +1,7 @@
---
title: System Variables
summary: Use system variables to optimize performance or alter running behavior.
category: reference
aliases: ['/tidb/stable/tidb-specific-system-variables','/docs/stable/system-variables/','/docs/v4.0/system-variables/','/docs/stable/reference/configuration/tidb-server/mysql-variables/','/docs/stable/tidb-specific-system-variables/','/docs/v4.0/tidb-specific-system-variables/','/docs/stable/reference/configuration/tidb-server/tidb-specific-variables/']
aliases: ['/tidb/stable/tidb-specific-system-variables','/docs/stable/system-variables/','/docs/v4.0/system-variables/','/docs/stable/reference/configuration/tidb-server/mysql-variables/','/docs/stable/tidb-specific-system-variables/','/docs/v4.0/tidb-specific-system-variables/','/docs/stable/reference/configuration/tidb-server/tidb-specific-variables/','/tidb/stable/tidb-specific-system-variables']
---

# System Variables
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12 changes: 12 additions & 0 deletions tidb-configuration-file.md
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Expand Up @@ -355,6 +355,18 @@ Configuration items related to performance.
- Default: `NO_PRIORITY`
- Optional values: `NO_PRIORITY`, `LOW_PRIORITY`, `HIGH_PRIORITY` and `DELAYED`.

### `distinct-agg-push-down`

- Determines whether the optimizer executes the operation that pushes down the aggregation function with `Distinct` (such as `select count(distinct a) from t`) to Coprocessors.
- Default: `false`
- This variable is the initial value of the system variable [`tidb_opt_distinct_agg_push_down`](/system-variables.md#tidb_opt_distinct_agg_push_down).

### `nested-loop-join-cache-capacity`

+ The maximum memory usage for the Least Recently Used (LRU) algorithm of the nested loop join cache (in bytes).
+ Default value: `20971520`
+ When `nested-loop-join-cache-capacity` is set to `0`, nested loop join cache is disabled by default. When the LRU size is larger than the value of `nested-loop-join-cache-capacity`, the elements in the LRU are removed.

## prepared-plan-cache

The Plan Cache configuration of the `PREPARE` statement.
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