add system variable back for tidb_enable_point_get_plan_cache. (#20679) (#20723)

Author: ti-chi-bot

system-variables.md

@@ -2547,6 +2547,14 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 
 </CustomContent>
 
+### tidb_enable_point_get_cache
+
+- Scope: SESSION
+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): YES
+- Type: Boolean
+- Default value: `OFF`
+- When you set the table lock type of [`LOCK TABLES`](/sql-statements/sql-statement-lock-tables-and-unlock-tables.md) to `READ`, setting this variable to `ON` enables caching of point query results, reducing the overhead of repeated queries and improving point query performance.
+
 ### tidb_enable_prepared_plan_cache <span class="version-mark">New in v6.1.0</span>
 
 - Scope: SESSION | GLOBAL