[docs](conf) add configuration for decommission_tablet_check_thres…

docs/en/docs/admin-manual/config/fe-config.md

@@ -413,6 +413,18 @@ MasterOnly：true
    3. After the decommission operation is completed, the BE will not be dropped. At this time, cancel the decommission status of the BE. Then the data will start to balance from other BE nodes back to this node. At this time, the data will be evenly distributed to all disks of the BE.
    4. Perform steps 2 and 3 for all BE nodes in sequence, and finally achieve the purpose of disk balancing for all nodes
 
+### decommission_tablet_check_threshold
+
+Default：5000
+
+IsMutable：true
+
+MasterOnly：true
+
+This configuration is used to control whether the Master FE need to check the status of tablets on decommissioned BE. If the size of tablets on decommissioned BE is lower than this threshold, FE will start a periodic check, if all tablets on decommissioned BE have been recycled, FE will drop this BE immediately.
+
+For performance consideration, please don't set a very high value for this configuration.
+
 ### period_of_auto_resume_min
 
 Default：5 （s）

docs/zh-CN/docs/admin-manual/config/fe-config.md

@@ -399,6 +399,18 @@ show data （其他用法：HELP SHOW DATA）
 3. decommission 操作完成后，该 BE 不会被删除。此时，取消掉该 BE 的 decommission 状态。则数据会开始从其他 BE 节点均衡回这个节点。此时，数据将会均匀的分布到该 BE 的所有磁盘上。
 4. 对所有 BE 节点依次执行 2，3 两个步骤，最终达到所有节点磁盘均衡的目的。
 
+### `decommission_tablet_check_threshold`
+
+默认值: 5000
+
+是否可以动态配置: true
+
+是否为 Master FE 节点独有的配置项：true
+
+该配置用于控制FE是否执行检测（Decommission）BE上Tablets状态的阈值。如果（Decommission）BE上的Tablets个数大于0但小于该阈值，FE会定时对该BE开启一项检测，
+
+如果该BE上的Tablets数量大于0但是所有Tablets均处于被回收的状态，那么FE会立即下线该（Decommission）BE。注意，不要把该值配置的太大，不然在Decommission阶段可能会对FE造成性能压力。
+
 ### `period_of_auto_resume_min`
 
 默认值：5 （s）