Add/clarify SQL length limits (#15602) (#15806)

pingcap · Dec 20, 2023 · 79d5fdd · 79d5fdd
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diff --git a/dashboard/dashboard-slow-query.md b/dashboard/dashboard-slow-query.md
@@ -59,6 +59,10 @@ Click any item in the list to display detailed execution information of the slow
 
 ### SQL
 
+> **Note:**
+>
+> The maximum length of the query recorded in the `Query` column is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable.
+
 Click the **Expand** button to view the detailed information of an item. Click the **Copy** button to copy the detailed information to the clipboard.
 
 ### Execution plans

diff --git a/information-schema/information-schema-slow-query.md b/information-schema/information-schema-slow-query.md
@@ -106,6 +106,8 @@ The output is as follows:
 74 rows in set (0.001 sec)
 ```
 
+The maximum statement length of the `Query` column is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable.
+
 ## CLUSTER_SLOW_QUERY table
 
 The `CLUSTER_SLOW_QUERY` table provides the slow query information of all nodes in the cluster, which is the parsing result of the TiDB slow log files. You can use the `CLUSTER_SLOW_QUERY` table the way you do with `SLOW_QUERY`. The table schema of the `CLUSTER_SLOW_QUERY` table differs from that of the `SLOW_QUERY` table in that an `INSTANCE` column is added to `CLUSTER_SLOW_QUERY`. The `INSTANCE` column represents the TiDB node address of the row information on the slow query.
@@ -222,9 +224,9 @@ The output is as follows:
 | id                         | estRows  | task      | access object            | operator info                                        |
 +----------------------------+----------+-----------+--------------------------+------------------------------------------------------+
 | StreamAgg_7                | 1.00     | root      |                          | funcs:count(1)->Column#75                            |
-| └─TableReader_13       | 10.00    | root      |                          | data:Selection_12                                    |
-|   └─Selection_12       | 10.00    | cop[tidb] |                          | eq(INFORMATION_SCHEMA.cluster_slow_query.user, "u1") |
-|     └─TableFullScan_11 | 10000.00 | cop[tidb] | table:CLUSTER_SLOW_QUERY | keep order:false, stats:pseudo                       |
+| └─TableReader_13           | 10.00    | root      |                          | data:Selection_12                                    |
+|   └─Selection_12           | 10.00    | cop[tidb] |                          | eq(INFORMATION_SCHEMA.cluster_slow_query.user, "u1") |
+|     └─TableFullScan_11     | 10000.00 | cop[tidb] | table:CLUSTER_SLOW_QUERY | keep order:false, stats:pseudo                       |
 +----------------------------+----------+-----------+--------------------------+------------------------------------------------------+
 4 rows in set (0.00 sec)
 ```

diff --git a/system-variables.md b/system-variables.md
@@ -4588,7 +4588,18 @@ For details, see [Identify Slow Queries](/identify-slow-queries.md).
 - Type: Integer
 - Default value: `4096`
 - Range: `[0, 2147483647]`
-- This variable is used to control the length of the SQL string in [statement summary tables](/statement-summary-tables.md).
+
+<CustomContent platform="tidb">
+
+- This variable is used to control the length of the SQL string in [statement summary tables](/statement-summary-tables.md), the [`SLOW_QUERY`](/information-schema/information-schema-slow-query.md) table, and the [TiDB Dashboard](/dashboard/dashboard-intro.md).
+
+</CustomContent>
+
+<CustomContent platform="tidb-cloud">
+
+- This variable is used to control the length of the SQL string in [statement summary tables](/statement-summary-tables.md) and the [`SLOW_QUERY`](/information-schema/information-schema-slow-query.md) table.
+
+</CustomContent>
 
 ### tidb_stmt_summary_max_stmt_count <span class="version-mark">New in v4.0</span>