Atomically transfer a key from a source Redis instance to a destination Redis instance. On success the key is deleted from the original instance and is guaranteed to exist in the target instance.
The command is atomic and blocks the two instances for the time required to transfer the key, at any given time the key will appear to exist in a given instance or in the other instance, unless a timeout error occurs. In 3.2 and above, multiple keys can be pipelined in a single call to MIGRATE by passing the empty string ("") as key and adding the KEYS clause.
The command internally uses DUMP to generate the serialized version of the key value, and RESTORE in order to synthesize the key in the target instance. The source instance acts as a client for the target instance. If the target instance returns OK to the RESTORE command, the source instance deletes the key using DEL.
The timeout specifies the maximum idle time in any moment of the communication with the destination instance in milliseconds. This means that the operation does not need to be completed within the specified amount of milliseconds, but that the transfer should make progresses without blocking for more than the specified amount of milliseconds.
MIGRATE needs to perform I/O operations and to honor the specified timeout.
When there is an I/O error during the transfer or if the timeout is reached the
operation is aborted and the special error - IOERR returned.
When this happens the following two cases are possible:
- The key may be on both the instances.
- The key may be only in the source instance.
It is not possible for the key to get lost in the event of a timeout, but the client calling MIGRATE, in the event of a timeout error, should check if the key is also present in the target instance and act accordingly.
When any other error is returned (starting with ERR) MIGRATE guarantees that
the key is still only present in the originating instance (unless a key with the
same name was also already present on the target instance).
If there are no keys to migrate in the source instance NOKEY is returned.
Because missing keys are possible in normal conditions, from expiry for example,
NOKEY isn't an error.
*Options
COPY-- Do not remove the key from the local instance.REPLACE-- Replace existing key on the remote instance.
COPY and REPLACE are available only in 3.0 and above.
*Return value
Simple string reply: The command returns OK on success, or NOKEY if no keys were
found in the source instance.