Redis ROLE 命令返回实例在复制中担任的角色， 这个角色可以是
sentinel 。 除了角色之外， 命令还会返回与该角色相关的其他信息， 其中：
- 主服务器将返回属下从服务器的 IP 地址和端口。
- 从服务器将返回自己正在复制的主服务器的 IP 地址、端口、连接状态以及复制偏移量。
- Sentinel 将返回自己正在监视的主服务器列表。
The command returns an array of elements. The first element is the role of the instance, as one of the following three strings:
The additional elements of the array depends on the role.
An example of output when ROLE is called in a master instance:
1) "master" 2) (integer) 3129659 3) 1) 1) "127.0.0.1" 2) "9001" 3) "3129242" 2) 1) "127.0.0.1" 2) "9002" 3) "3129543"
The master output is composed of the following parts:
- The string
- The current master replication offset, which is an offset that masters and replicas share to understand, in partial resynchronizations, the part of the replication stream the replicas needs to fetch to continue.
- An array composed of three elements array representing the connected replicas. Every sub-array contains the replica IP, port, and the last acknowledged replication offset.
*Output of the command on replicas
An example of output when ROLE is called in a replica instance:
1) "slave" 2) "127.0.0.1" 3) (integer) 9000 4) "connected" 5) (integer) 3167038
The replica output is composed of the following parts:
- The string
slave, because of backward compatibility (see note at the end of this page).
- The IP of the master.
- The port number of the master.
- The state of the replication from the point of view of the master, that can be
connect(the instance needs to connect to its master),
connecting(the master-replica connection is in progress),
sync(the master and replica are trying to perform the synchronization),
connected(the replica is online).
- The amount of data received from the replica so far in terms of master replication offset.
An example of Sentinel output:
1) "sentinel" 2) 1) "resque-master" 2) "html-fragments-master" 3) "stats-master" 4) "metadata-master"
The sentinel output is composed of the following parts:
- The string
- An array of master names monitored by this Sentinel instance.
数组: where the first element is one of
sentinel and the additional elements are role-specific as illustrated above.
- This command was introduced in the middle of a Redis stable release, specifically with Redis 2.8.12.
1) "master" 2) (integer) 0 3) (empty list or set)
A note about the word slave used in this man page: Starting with Redis 5, if not for backward compatibility, the Redis project no longer uses the word slave. Unfortunately in this command the word slave is part of the protocol, so we'll be able to remove such occurrences only when this API will be naturally deprecated.