Fix performance degradation due to non-caching of command info in Redis 6 Cluster

[yuuki]

What is the problem?

I observed performance degradation when using redis.ClusterClient in Redis 6.
pprof reported the following bottleneck caused by mutex lock (https://github.com/go-redis/redis/blob/a999d1ecd81303df8128547746c62358f78048f5/command.go#L2153-L2154).

This mutex lock is for the client to cache COMMAND reply just once (https://github.com/go-redis/redis/blob/a999d1ecd81303df8128547746c62358f78048f5/cluster.go#L688).
However, I noticed that during the debugging of this performance degradation problem, for some reason the client executed COMMAND command every time.

What caused the problem?

I got the following error that has already reported in #1329 in Redis 6.

redis: got 7 elements in COMMAND reply, wanted 6

This error prevented the internal.once from setting the done flag
(https://github.com/go-redis/redis/blob/a999d1ecd81303df8128547746c62358f78048f5/internal/once.go#L54-L57). As a result, the client did not cache COMMAND reply.

This error is caused by the change of additional command categories in Redis 6.
I show the example of the output of COMMAND and COMMAND INFO reply.

• Redis 5.0.8 (6 elements)

127.0.0.1:6379> COMMAND INFO xadd
1) 1) "xadd"
   2) (integer) -5
   3) 1) write
      2) denyoom
      3) random
      4) fast
   4) (integer) 1
   5) (integer) 1
   6) (integer) 1

• Redis 6.0.1 (7 elements)

127.0.0.1:6379> COMMAND INFO xadd
1) 1) "xadd"
   2) (integer) -5
   3) 1) write
      2) denyoom
      3) random
      4) fast
   4) (integer) 1
   5) (integer) 1
   6) (integer) 1
   7) 1) @write
      2) @stream
      3) @fast

Thus, I have fixed go-redis to handle this 7th elements for additional ACL categories. Finally, I solved my problem of performance degradation.

[vmihailenco]

Thanks for the PR - I've merged this a part of #1357

[yuuki]

Thanks for your quick response!