sysvar: add variables in 6.4 doc (pingcap#11229)

Author: TomShawn

system-variables.md

@@ -660,6 +660,17 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
 - Default value: `OFF`
 - This variable is used to set whether the `AUTO_INCREMENT` property of a column is allowed to be removed by executing `ALTER TABLE MODIFY` or `ALTER TABLE CHANGE` statements. It is not allowed by default.
 
+### tidb_analyze_partition_concurrency
+
+> **Warning:**
+>
+> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.
+
+- Scope: SESSION | GLOBAL
+- Persists to cluster: Yes
+- Default value: `1`
+- This variable specifies the concurrency of reading and writing statistics for a partitioned table when TiDB analyzes the partitioned table.
+
 ### tidb_analyze_version <span class="version-mark">New in v5.1.0</span>
 
 - Scope: SESSION | GLOBAL
@@ -1451,6 +1462,14 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
 - Default value: `OFF`
 - This variable controls whether to enable the General Plan Cache feature.
 
+### tidb_enable_gogc_tuner <span class="version-mark">New in v6.4.0</span>
+
+- Scope: GLOBAL
+- Persists to cluster: No, only applicable to the current TiDB instance that you are connecting to.
+- Type: Boolean
+- Default value: `ON`
+- This variable controls whether to enable GOGC Tuner.
+
 ### tidb_enable_historical_stats
 
 - Scope: GLOBAL
@@ -2149,6 +2168,14 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - When this variable is set to `ON`, you can view visual execution plans in TiDB Dashboard. Note that TiDB Dashboard only provides visual display for execution plans generated after this variable is enabled.
 - You can execute the `SELECT tidb_decode_binary_plan('xxx...')` statement to parse the specific plan from a binary plan.
 
+### tidb_gogc_tuner_threshold <span class="version-mark">New in v6.4.0</span>
+
+- Scope: GLOBAL
+- Persists to cluster:  No, only applicable to the current TiDB instance that you are connecting to.
+- Default value: `0.6`
+- Range: `[0, 0.9)`
+- This variable specifies the maximum memory threshold for tuning GOGC. When the memory exceeds this threshold, GOGC Tuner stops working.
+
 ### tidb_guarantee_linearizability <span class="version-mark">New in v5.0</span>
 
 - Scope: SESSION | GLOBAL
@@ -2581,6 +2608,17 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - This variable sets the concurrency of the `MergeJoin` operator when a query is executed.
 - It is **NOT recommended** to set this variable. Modifying the value of this variable might cause data correctness issues.
 
+### tidb_merge_partition_stats_concurrency
+
+> **Warning:**
+>
+> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.
+
+- Scope: SESSION | GLOBAL
+- Persists to cluster: Yes
+- Default value: `1`
+- This variable specifies the concurrency of merging statistics for a partitioned table when TiDB analyzes the partitioned table.
+
 ### tidb_metric_query_range_duration <span class="version-mark">New in v4.0</span>
 
 <CustomContent platform="tidb-cloud">