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update statement summary variables scope (#8268) #8613

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ti-chi-bot merged 1 commit into from
May 13, 2022
Merged

update statement summary variables scope (#8268) #8613

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7 changes: 0 additions & 7 deletions statement-summary-tables.md
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Expand Up @@ -130,13 +130,6 @@ After the configuration above takes effect, every 30 minutes the `statements_sum

The `statements_summary_evicted` table records the recent 24 periods during which SQL statements are evicted from the statement summary. The `statements_summary_evicted` table is updated every 30 minutes.

The system variables above have two scopes: global and session. These scopes work differently from other system variables:

- After setting the global variable, your setting applies to the whole cluster immediately.
- After setting the session variable, your setting applies to the current TiDB server immediately. This is useful when you debug on a single TiDB server instance.
- The session variable has a higher read priority. The global variable is read only when no session variable is set.
- If you set the session variable to a blank string, the global variable is re-read.

> **Note:**
>
> The `tidb_stmt_summary_history_size`, `tidb_stmt_summary_max_stmt_count`, and `tidb_stmt_summary_max_sql_length` configuration items affect memory usage. It is recommended that you adjust these configurations based on your needs. It is not recommended to set them too large values.
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