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br: add variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag (#21481) #22239

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br: add variable tidb_advancer_check_point_lag_limit to control log backup checkpoint lag (#21481) #22239

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Leavrth Jul 31, 2025
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Update system-variables.md
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hfxsd Aug 5, 2025
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hfxsd Dec 25, 2025
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10 changes: 10 additions & 0 deletions system-variables.md
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Expand Up @@ -1012,6 +1012,16 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count';
- Unit: Bytes
- This variable is used to control the threshold at which the TiDB server prefers to send read requests to a replica in the same availability zone as the TiDB server when [`tidb_replica_read`](#tidb_replica_read-new-in-v40) is set to `closest-adaptive`. If the estimated result is higher than or equal to this threshold, TiDB prefers to send read requests to a replica in the same availability zone. Otherwise, TiDB sends read requests to the leader replica.

### tidb_advancer_check_point_lag_limit <span class="version-mark">New in v8.5.5</span>

- Scope: GLOBAL
- Persists to cluster: Yes
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
- Type: Duration
- Default value: `48h0m0s`
- Range: `[1s, 8760h0m0s]`
- This variable controls the maximum allowed checkpoint lag for a log backup task. If a task's checkpoint lag exceeds this limit, TiDB Advancer pauses the task.
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For better clarity and consistency with other variable descriptions, consider replacing the internal component name 'TiDB Advancer' with 'TiDB'. This makes the documentation easier for users to understand, as 'TiDB Advancer' is not defined elsewhere.

Suggested change
- This variable controls the maximum allowed checkpoint lag for a log backup task. If a task's checkpoint lag exceeds this limit, TiDB Advancer pauses the task.
- This variable controls the maximum allowed checkpoint lag for a log backup task. If a task's checkpoint lag exceeds this limit, TiDB pauses the task.
References
  1. The style guide emphasizes clarity and making documentation easy to understand for users (Lines 14, 21). The term 'TiDB Advancer' is not defined elsewhere and could be confusing. Using 'TiDB' is clearer and more consistent with other descriptions. (link)


### tidb_allow_tiflash_cop <span class="version-mark">New in v7.3.0</span>

- Scope: SESSION | GLOBAL
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