planner: add tidb_enable_binding_usage

system-variables.md

@@ -1937,6 +1937,15 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Default value: `OFF`
 - This variable controls whether to enable the deprecated batch-dml feature. When it is enabled, certain statements might be split into multiple transactions, which is non-atomic and should be used with care. When using batch-dml, you must ensure that there are no concurrent operations on the data you are operating on. To make it work, you must also specify a positive value for `tidb_batch_dml_size` and enable at least one of `tidb_batch_insert` and `tidb_batch_delete`.
 
+### tidb_enable_binding_usage <span class="version-mark">New in v9.0.0</span>
+
+- Scope: GLOBAL
+- Persists to cluster: Yes
+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
+- Type: Boolean
+- Default value: `ON`
+- This variable controls whether to enable the usage statistics collection for SQL plan bindings. When this variable is enabled, TiDB writes the usage information of SQL plan bindings to TiKV every six hours.
+
 ### tidb_enable_cascades_planner
 
 > **Warning:**