If you get an error that reads “WRONGTYPE Operation against a key holding the wrong kind of value” when using the ZMPOP or BZMPOP commands in Redis, it’s because you’re passing a key with the wrong data type.

To fix this issue, make sure you pass a sorted set to these commands.

Example of Error

Here’s an example of code that causes the error:

ZMPOP 1 countries MIN

Result:

(error) WRONGTYPE Operation against a key holding the wrong kind of value

In my case, the countries key holds a set (not a sorted set), which is why I got the error.

We can use the TYPE command to check a key’s type:

TYPE countries

Result:

set

As suspected, the key holds a set, which is the wrong data type for the ZMPOP command (and the BZMPOP command).

Solution

The solution is to make sure the keys we pass to ZMPOP (and BZMPOP) hold a sorted set.

Let’s replace the countries key with another key that holds a sorted set:

ZMPOP 1 cats MIN

Result:

1) "cats"
2) 1) 1) "Meow"
      2) "1"

This time we didn’t get the error. That’s because the cats key holds a sorted set.

Let’s check:

TYPE cats

Result:

zset

It’s a sorted set, as expected.