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system-variables: add @@global.tidb_accelerate_user_creation_update #19834

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system-variables: add @@global.tidb_accelerate_user_creation_update #19834

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11 changes: 11 additions & 0 deletions system-variables.md
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Expand Up @@ -869,6 +869,17 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count';
- 默认值：（随系统）
- 该变量显示首次引导启动 TiDB 时的系统时区。另请参阅 [`time_zone`](#time_zone)。

### `tidb_accelerate_user_creation_update` <span class="version-mark">从 v9.0.0 版本开始引入</span>

- 作用域：GLOBAL
- 是否持久化到集群：是
- 是否受 Hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value) 控制：否
- 类型：布尔型
- 默认值：`OFF`
- 当系统中创建的 SQL 用户数量过多(比如10万以上)之后，创建用户/修改密码/设置权限等一些操作会受到比较严重的性能影响。原因是每次用户更新会涉及重新加载全部用户数据，这样的场景下建议将该变量设置为 `ON`。
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打开有什么副作用需要说明么？

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打开完全没有任何副作用...
感觉下个版本默认打开算了

* `0` 或 `OFF`：修改用户相关的操作会导致重新加载全部用户数据到内存，性能较差。
* `1` 或 `ON`：修改用户只会更新当前活跃的用户，性能更优。

### `tidb_adaptive_closest_read_threshold` <span class="version-mark">从 v6.3.0 版本开始引入</span>

- 作用域：SESSION | GLOBAL
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