[BUG] Memory metric db.dict.rehashing.count breaks older clients

[JimB123]

Describe the bug

Using the MEMORY STATS command, older clients use db.x to recognize a substructure related to a specific database. Like db.0 has values containing overhead.hashtable.main and overhead.hashtable.expires.

Unfortunately, a new metric named db.dict.rehashing.count breaks older clients due to the prefix of db.. This makes it impossible to execute MEMORY STATS from these clients.

Specifically, in python-redis, in function parse_memory_stats, a line of code was changed:

        if key.startswith("db."):                              # OLD
        if key.startswith("db.") and isinstance(value, list):  # NEW

Recommend renaming this metric to avoid the use of db. as a prefix.

To reproduce

Use an older version of python-redis and execute: client.memory_stats(). It will throw an exception.

Expected behavior

No exception

[JimB123]

Also recommend adding a test which executes MEMORY STATS to prevent future similar issues.

[enjoy-binbin]

Recommend renaming this metric to avoid the use of db. as a prefix.

Sadly changing this is a breaking change...

[madolson]

Yeah, it was also a change we inherited from Redis: redis/redis#12913. I'm not sure we can easily diverge at this point. It's probably we could we remember this to avoid doing this in the future, but I agree I think we need to keep it.