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br: introduce global variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag limitation #20710

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br: introduce global variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag limitation #20710

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Expand Up @@ -908,6 +908,16 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count';
- 单位：字节
- 这个变量用于控制当 [`replica-read`](#tidb_replica_read-从-v40-版本开始引入) 设置为 `closest-adaptive` 时，优先将读请求发送至 TiDB server 所在区域副本的阈值。当读请求预估的返回结果的大小超过此阈值时，TiDB 会将读请求优先发送至同一可用区的副本，否则会发送至 leader 副本。

### `tidb_advancer_check_point_lag_limit` <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：Duration
- 默认值：`48h0m0s`
- 范围：`[1s, 8760h0m0s]`
- 这个变量用于控制日志备份任务 Checkpoint 的滞后时间限制。如果日志备份任务 Checkpoint 的滞后时间超过了该限制，TiDB Advancer 会暂停该任务。

### `tidb_allow_tiflash_cop` <span class="version-mark">从 v7.3.0 版本开始引入</span>

- 作用域：SESSION | GLOBAL
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