doc(stream): sink cache doc

docs/en_US/rules/overview.md

@@ -52,6 +52,9 @@ Currently, 3 kinds of actions are supported: [log](sinks/logs.md), [mqtt](sinks/
 | concurrency | int: 1   | Specify how many instances of the sink will be run. If the value is bigger than 1, the order of the messages may not be retained. |
 | bufferLength | int: 1024   | Specify how many messages can be buffered in memory. If the buffered messages exceed the limit, the sink will block message receiving until the buffered messages have been sent out so that the buffered size is less than the limit. |
 | runAsync        | bool:false   | Whether the sink will run asynchronously for better performance. If it is true, the sink result order is not promised.  |
+| retryInterval   | int:1000   | Specify how many milliseconds will the sink retry to send data out if the previous send failed  |
+| cacheLength     | int:10240   | Specify how many messages can be cached. The cached messages will be resent to external system until the data sent out successfully. The cached message will be sent in order except in runAsync or concurrent mode. The cached message will be saved to disk in fixed intervals.  |
+| cacheSaveInterval  | int:1000   | Specify the interval to save cached message to the disk. Notice that, if the rule is closed in plan, all the cached messages will be saved at close. A larger value can reduce the saving overhead but may lose more cache messages when the system is interrupted in error.  |
 
 Actions could be customized to support different kinds of outputs, see [extension](../extension/overview.md) for more detailed info.
 

docs/zh_CN/rules/overview.md

@@ -52,6 +52,9 @@
 | concurrency | int: 1   | 设置运行的线程数。该参数值大于1时，消息发出的顺序可能无法保证。 |
 | bufferLength | int: 1024   | 设置可缓存消息数目。若缓存消息数超过此限制，sink将阻塞消息接收，直到缓存消息被消费使得缓存消息数目小于限制为止。|
 | runAsync        | bool:false   | 设置是否异步运行输出操作以提升性能。请注意，异步运行的情况下，输出结果顺序不能保证。  |
+| retryInterval   | int:1000   | 设置信息发送失败后重试等待时间，单位为毫秒|
+| cacheLength     | int:10240   | 设置最大消息缓存数量。缓存的消息会一直保留直到消息发送成功。缓存消息将按顺序发送，除非运行在异步或者并发模式下。缓存消息会定期存储到磁盘中。  |
+| cacheSaveInterval  | int:1000   | 设置缓存存储间隔时间，单位为毫秒。需要注意的是，当规则关闭时，缓存会自动存储。该值越大，则缓存保存开销越小，但系统意外退出时缓存丢失的风险变大。 |
 
 可以自定义动作以支持不同种类的输出，有关更多详细信息，请参见 [extension](../extension/overview.md) 。