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Revert "Revert "v8.5.6: system-variables: add doc for `tidb_max_dist_… #22673

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16 changes: 16 additions & 0 deletions system-variables.md
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Expand Up @@ -3888,6 +3888,22 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
- Range: `[100, 16384]`
- This variable is used to set the maximum number of schema versions (the table IDs modified for corresponding versions) allowed to be cached. The value range is 100 ~ 16384.

### tidb_max_dist_task_nodes <span class="version-mark">New in v8.5.6</span>

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
- Type: Integer
- Default value: `-1`
- Range: `-1` or `[1, 128]`
- This variable defines the maximum number of TiDB nodes that the Distributed eXecution Framework (DXF) tasks can use. The default value is `-1`, which indicates that automatic mode is enabled. In automatic mode, TiDB dynamically calculates the value as `min(3, tikv_nodes / 3)`, where `tikv_nodes` represents the number of TiKV nodes in the cluster.
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Improve clarity and conciseness by removing redundant words and using 'is' instead of 'represents'. Also, use 'In this mode' to avoid repetition of 'automatic mode'.

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- This variable defines the maximum number of TiDB nodes that the Distributed eXecution Framework (DXF) tasks can use. The default value is `-1`, which indicates that automatic mode is enabled. In automatic mode, TiDB dynamically calculates the value as `min(3, tikv_nodes / 3)`, where `tikv_nodes` represents the number of TiKV nodes in the cluster.
- This variable defines the maximum number of TiDB nodes that Distributed eXecution Framework (DXF) tasks can use. The default value `-1` indicates that automatic mode is enabled. In this mode, TiDB dynamically calculates the value as `min(3, tikv_nodes / 3)`, where `tikv_nodes` is the number of TiKV nodes in the cluster.
References
  1. Avoid unnecessary words and repetition. (link)


> **Note:**
>
> If you explicitly set the [`tidb_service_scope`](#tidb_service_scope-new-in-v740) system variable for some TiDB nodes, the Distributed eXecution Framework schedules tasks only to these nodes. In this case, even if you set `tidb_max_dist_task_nodes` to a larger value, the framework uses no more than the number of nodes explicitly configured with `tidb_service_scope`.
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Use the acronym 'DXF' for consistency and 'at most' for better readability. Also, address the user directly as per the style guide.

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> If you explicitly set the [`tidb_service_scope`](#tidb_service_scope-new-in-v740) system variable for some TiDB nodes, the Distributed eXecution Framework schedules tasks only to these nodes. In this case, even if you set `tidb_max_dist_task_nodes` to a larger value, the framework uses no more than the number of nodes explicitly configured with `tidb_service_scope`.
> If you explicitly set the [`tidb_service_scope`](#tidb_service_scope-new-in-v740) system variable for some TiDB nodes, DXF schedules tasks only to these nodes. In this case, even if you set `tidb_max_dist_task_nodes` to a larger value, DXF uses at most the number of nodes you explicitly configured with `tidb_service_scope`.
References
  1. Write in second person ("you") when addressing users. (link)
  2. Use consistent terminology. (link)

>
> For example, if the cluster has 10 TiDB nodes, and 4 of them are configured with `tidb_service_scope = group1`, then even if you set `tidb_max_dist_task_nodes = 5`, only 4 nodes participate in task execution.
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Minor grammatical improvement for better flow and clarity.

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> For example, if the cluster has 10 TiDB nodes, and 4 of them are configured with `tidb_service_scope = group1`, then even if you set `tidb_max_dist_task_nodes = 5`, only 4 nodes participate in task execution.
> For example, if the cluster has 10 TiDB nodes and 4 of them are configured with `tidb_service_scope = group1`, then even if you set `tidb_max_dist_task_nodes = 5`, only 4 nodes participate in the task execution.


### tidb_max_paging_size <span class="version-mark">New in v6.3.0</span>

- Scope: SESSION | GLOBAL
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