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

* cherry pick #3259 to release-4.0 Signed-off-by: ti-srebot <ti-srebot@pingcap.com> * resolve conflict * resolve conflict Co-authored-by: Ran <huangran@pingcap.com>
pingcap · Jul 14, 2020 · 2f1a089 · 2f1a089
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diff --git a/system-variables.md b/system-variables.md
@@ -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

diff --git a/tidb-configuration-file.md b/tidb-configuration-file.md
@@ -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.