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Add/clarify SQL length limits #15602

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Dec 20, 2023
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Add/clarify SQL length limits #15602

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7a50c63
Add/clarify SQL length limits
dveeden Dec 5, 2023
5215938
Update with TiDB/Cloud differences
dveeden Dec 5, 2023
109a32f
Fix MD012
dveeden Dec 5, 2023
384c08c
Update system-variables.md
dveeden Dec 14, 2023
38c5b0b
Update dashboard/dashboard-slow-query.md
dveeden Dec 14, 2023
3d5202b
Update system-variables.md
dveeden Dec 14, 2023
18bf600
Update system-variables.md
dveeden Dec 19, 2023
447d92a
Update system-variables.md
dveeden Dec 19, 2023
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4 changes: 4 additions & 0 deletions dashboard/dashboard-slow-query.md
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Expand Up @@ -60,6 +60,10 @@ Click any item in the list to display detailed execution information of the slow

### SQL

> **Note:**
>
> The maximum length of the query is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable.
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### Execution plans
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8 changes: 5 additions & 3 deletions information-schema/information-schema-slow-query.md
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Expand Up @@ -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.
Expand Down Expand Up @@ -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)
```
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9 changes: 8 additions & 1 deletion system-variables.md
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Expand Up @@ -5230,7 +5230,14 @@ 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">
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- 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 on the [TiDB Dashboard](/dashboard/dashboard-intro.md).
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</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.
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</CustomContent>
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### tidb_stmt_summary_max_stmt_count <span class="version-mark">New in v4.0</span>

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