Returns the number of entries inside a stream. If the specified key does not exist the command returns zero, as if the stream was empty. However note that unlike other Redis types, zero-length streams are possible, so you should call TYPE or EXISTS in order to check if a key exists or not.
Streams are not auto-deleted once they have no entries inside (for instance after an XDEL call), because the stream may have consumer groups associated with it.
*返回值
整数: the number of entries of the stream at key.
*例子
redis>
XADD mystream * item 1
"1732205552967-0"redis> XADD mystream * item 2
"1732205552968-0"redis> XADD mystream * item 3
"1732205552968-1"redis> XLEN mystream
(integer) 3