planner: add doc for tidb_ignore_inlist_plan_digest. (#20870) (#20889)

Author: ti-chi-bot

releases/release-7.6.0.md

@@ -272,6 +272,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v7.6/quick-start-with-
 | [`tidb_ddl_version`](https://docs.pingcap.com/tidb/v7.6/system-variables#tidb_ddl_version-new-in-v760)  |  Newly added  | Controls whether to enable [TiDB DDL V2](https://docs.pingcap.com/tidb/v7.6/ddl-v2). Set the value to `2` to enable it and `1` to disable it. The default value is `1`. When TiDB DDL V2 is enabled, DDL statements will be executed using TiDB DDL V2. The execution speed of DDL statements for creating tables is increased by 10 times compared with TiDB DDL V1. |
 | [`tidb_enable_global_index`](/system-variables.md#tidb_enable_global_index-new-in-v760)  |  Newly added   | Controls whether to support creating `Global indexes` for partitioned tables. The default value is `OFF`. `Global index` is currently in the development stage. **It is not recommended to modify the value of this system variable**. |
 | [`tidb_idle_transaction_timeout`](/system-variables.md#tidb_idle_transaction_timeout-new-in-v760) | Newly added | Controls the idle timeout for transactions in a user session. When a user session is in a transactional state and remains idle for a duration exceeding the value of this variable, TiDB will terminate the session. The default value `0` means unlimited. |
+| [`tidb_ignore_inlist_plan_digest`](/system-variables.md#tidb_ignore_inlist_plan_digest-new-in-v760) | Newly added | Controls whether TiDB ignores the element differences in the `IN` list across different queries when generating Plan Digests. The default value `OFF` means differences are not ignored. |
 | [`tidb_opt_enable_fuzzy_binding`](/system-variables.md#tidb_opt_enable_fuzzy_binding-new-in-v760) | Newly added | Controls whether to enable the cross-database binding feature. The default value `OFF` means cross-database binding is disabled. |
 | [`tidb_txn_entry_size_limit`](/system-variables.md#tidb_txn_entry_size_limit-new-in-v760) | Newly added | Dynamically modifies the TiDB configuration item [`performance.txn-entry-size-limit`](/tidb-configuration-file.md#txn-entry-size-limit-new-in-v4010-and-v500). It limits the size of a single row of data in TiDB. The default value of this variable is `0`, which means that TiDB uses the value of the configuration item `txn-entry-size-limit` by default. When this variable is set to a non-zero value, `txn-entry-size-limit` is also set to the same value. |
 | [`pd_enable_follower_handle_region`](/system-variables.md#pd_enable_follower_handle_region-new-in-v760) | Newly added | Controls whether to enable the [Active PD Follower](/tune-region-performance.md#use-the-active-pd-follower-feature-to-enhance-the-scalability-of-pds-region-information-query-service) feature (experimental). When the value is `OFF`, TiDB only obtains Region information from the PD leader. When the value is `ON`, TiDB evenly distributes requests for Region information to all PD servers, and PD followers can also handle Region requests, thereby reducing the CPU pressure on the PD leader. |

system-variables.md

@@ -3315,6 +3315,18 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - This variable is used to set whether to ignore the commands for closing prepared statement cache.
 - When this variable is set to `ON`, the `COM_STMT_CLOSE` command of the Binary protocol and the [`DEALLOCATE PREPARE`](/sql-statements/sql-statement-deallocate.md) statement of the text protocol are ignored. For details, see [Ignore the `COM_STMT_CLOSE` command and the `DEALLOCATE PREPARE` statement](/sql-prepared-plan-cache.md#ignore-the-com_stmt_close-command-and-the-deallocate-prepare-statement).
 
+### tidb_ignore_inlist_plan_digest <span class="version-mark">New in v7.6.0</span>
+
+- Scope: GLOBAL
+- Persists to cluster: Yes
+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
+- Type: Boolean
+- Default value: `OFF`
+- This variable controls whether TiDB ignores the element differences in the `IN` list across different queries when generating Plan Digests.
+
+    - When it is the default value `OFF`, TiDB does not ignore the element differences (including the difference in the number of elements) in the `IN` list when generating Plan Digests. The element differences in the `IN` list result in different Plan Digests.
+    - When it is set to `ON`, TiDB ignores the element differences (including the difference in the number of elements) in the `IN` list and uses `...` to replace elements in the `IN` list in Plan Digests. In this case, TiDB generates the same Plan Digests for `IN` queries of the same type.
+
 ### tidb_index_join_batch_size
 
 - Scope: SESSION | GLOBAL