How to delete keys matching a pattern in Redis Cluster

Question

I have tried method in this question, but it does not work since I'm working in cluster mode, and redis told me:

(error) CROSSSLOT Keys in request don't hash to the same slot

Answer 1

Answers for that question try to remove multiple keys in a single DEL. However, keys matching the given pattern might NOT locate in the same slot, and Redis Cluster DOES NOT support multiple-key command if these keys don't belong to the same slot. That's why you get the error message.

In order to fix this problem, you need to DEL these keys one-by-one:

redis-cli --scan --pattern "foo*" |xargs -L 1 redis-cli del

The -L option for xargs command specifies the number of keys to delete. You need to specify this option as 1.

In order to remove all keys matching the pattern, you also need to run the above command for every master nodes in your cluster.

NOTE

1. With this command, you have to delete these keys one-by-one, and that might be very slow. You need to consider re-designing your database, and use hash-tags to make keys matching the pattern belong to the same slot. So that you can remove these keys in a single DEL.

2. Either SCAN or KEYS command are inefficient, especially, KEYS should not be used in production. You need to consider building an index for these keys.

Answer 2

Building on for_stack's answer, you can speed up mass deletion quite a bit using redis-cli --pipe, and reduce the performance impact with UNLINK instead of DEL if you're using redis 4 or higher.

redis-cli --scan --pattern "foo*" | xargs -L 1 echo UNLINK | redis-cli --pipe

Output will look something like this:

All data transferred. Waiting for the last reply...
Last reply received from server.
errors: 0, replies: 107003

You do still need to run this against every master node in your cluster. If you have a large number of nodes, it's probably possible to automate the process further by parsing the output of CLUSTER NODES.