Redis CROSSSLOT Keys in request don't hash to the same slot

What is Redis CROSSSLOT Keys in request don't hash to the same slot

When encountering the CROSSSLOT Keys in request don't hash to the same slot error in Redis, especially in a clustered environment, it implies that the operation involves multiple keys that do not hash to the same slot, violating Redis Cluster's requirement for multi-key operations to act on keys within the same slot.

Immediate Actions:

Identify the Keys and Their Slots:Use the CLUSTER KEYSLOT command for each key involved in the operation to determine their respective slots. For example, to find the slot for key "mykey", you would run:CLUSTER KEYSLOT mykeyAnalyze the Key Distribution:If you have a small set of keys, manually check if they belong to different slots. For operations involving multiple keys (like MGET, MSET, SUNION, etc.), all keys must hash to the same slot.Use Hash Tags:If possible, modify the keys to use hash tags. Redis supports a concept where part of the key name is enclosed in {} and only this part is considered for hashing. This ensures that keys with the same hash tag land in the same slot. For example, if you have keys like user:{123}:name and user:{123}:email, both will hash to the same slot because of the 123 hash tag. Modify your keys accordingly if you have control over the key names.Reroute the Command to the Correct Node:If you ran the command against a node that doesn't hold the slot for the key(s), use the CLUSTER NODES or CLUSTER SLOTS command to find the correct node that holds the slot and reroute your command to that node. For example:CLUSTER NODESorCLUSTER SLOTSThis information allows you to direct your command to the appropriate cluster node.

Note:

These actions are intended for immediate troubleshooting and mitigation. If you're not familiar with Redis Cluster's inner workings or the implications of these changes, proceed with caution and consult documentation or seek assistance if necessary.