stmtsummary: add system vars description

system-variables.md

@@ -3797,6 +3797,63 @@ For details, see [Identify Slow Queries](/identify-slow-queries.md).
 - Unit: Milliseconds
 - This variable controls whether to enable the synchronously loading statistics feature. The value `0` means that the feature is disabled. To enable the feature, you can set this variable to a timeout (in milliseconds) that SQL optimization can wait for at most to synchronously load complete column statistics. For details, see [Load statistics](/statistics.md#load-statistics).
 
+### tidb_stmt_summary_enable_persistent <span class="version-mark">New in v6.6.0</span>
+
+> **Warning:**
+>
+> Statements summary persistence is an experimental feature. It is not recommended that you use it in the production environment. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
+
+- Scope: GLOBAL
+- Type: Boolean
+- Default value: `false`
+- This variable is read-only. It controls whether to enable [statements summary persistence](/statement-summary-tables.md#persist-statements-summary). The value of this variable is the same as that of the configuration item [`tidb_stmt_summary_enable_persistent`](/tidb-configuration-file.md#tidb_stmt_summary_enable_persistent-new-in-v660).
+
+### tidb_stmt_summary_filename <span class="version-mark">New in v6.6.0</span>
+
+> **Warning:**
+>
+> Statements summary persistence is an experimental feature. It is not recommended that you use it in the production environment. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
+
+- Scope: GLOBAL
+- Type: String
+- Default value: `tidb-statements.log`
+- This variable is read-only. It specifies the file to which persistent data is written when [statements summary persistence](/statement-summary-tables.md#persist-statements-summary) is enabled. The value of this variable is the same as that of the configuration item [`tidb_stmt_summary_enable_persistent`](/tidb-configuration-file.md#tidb_stmt_summary_enable_persistent-new-in-v660).
+
+### tidb_stmt_summary_file_max_backups <span class="version-mark">New in v6.6.0</span>
+
+> **Warning:**
+>
+> Statements summary persistence is an experimental feature. It is not recommended that you use it in the production environment. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
+
+- Scope: GLOBAL
+- Type: Integer
+- Default value: `0`
+- This variable is read-only. It specifies the maximum number of data files that can be persisted. when [statements summary persistence](/statement-summary-tables.md#persist-statements-summary) is enabled. The value of this variable is the same as that of the configuration item [`tidb_stmt_summary_enable_persistent`](/tidb-configuration-file.md#tidb_stmt_summary_enable_persistent-new-in-v660).
+
+### tidb_stmt_summary_file_max_days <span class="version-mark">New in v6.6.0</span>
+
+> **Warning:**
+>
+> Statements summary persistence is an experimental feature. It is not recommended that you use it in the production environment. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
+
+- Scope: GLOBAL
+- Type: Integer
+- Default value: `3`
+- Unit: day
+- This variable is read-only. It specifies the maximum number of days to keep persistent data files when [statements summary persistence](/statement-summary-tables.md#persist-statements-summary) is enabled. The value of this variable is the same as that of the configuration item [`tidb_stmt_summary_enable_persistent`](/tidb-configuration-file.md#tidb_stmt_summary_enable_persistent-new-in-v660).
+
+### tidb_stmt_summary_file_max_size <span class="version-mark">New in v6.6.0</span>
+
+> **Warning:**
+>
+> Statements summary persistence is an experimental feature. It is not recommended that you use it in the production environment. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
+
+- Scope: GLOBAL
+- Type: Integer
+- Default value: `64`
+- Unit: MiB
+- This variable is read-only. It specifies the maximum size of a persistent data file when [statements summary persistence](/statement-summary-tables.md#persist-statements-summary) is enabled. The value of this variable is the same as that of the configuration item [`tidb_stmt_summary_enable_persistent`](/tidb-configuration-file.md#tidb_stmt_summary_enable_persistent-new-in-v660).
+
 ### tidb_stmt_summary_history_size <span class="version-mark">New in v4.0</span>
 
 - Scope: GLOBAL