Hi @antirez , we had a discussion about forbidden some commands in lua script in #4835.

But now I just found some commands are dangerous in multi/exec too... for instance:

We have a master instance listening on port 6379, and an replica listening on 7788, then execute REPLICAOF command in multi/exec on master:

127.0.0.1:6379> multi
OK
127.0.0.1:6379> replicaof 127.0.0.1 1234
QUEUED
127.0.0.1:6379> set a b
QUEUED
127.0.0.1:6379> set c d
QUEUED
127.0.0.1:6379> replicaof no one
QUEUED
127.0.0.1:6379> exec
1) OK
2) OK
3) OK
4) OK
127.0.0.1:6379> keys *
1) "c"
2) "a"

But the replica has nothing:

127.0.0.1:7788> keys *
(empty list or set)
127.0.0.1:7788> quit

It's because in multi/exec after REPLICAOF 127.0.0.1 1234 the master became an replica, then write commands would not be replicated, neither the repl_backlog.

So, I think we should forbid some replication commands like REPLICAOF, SYNC, PSYNC.

I know this is a corner case, but it really can lead to data inconsistency between master and replica.