Keys that have a large value. If the size of a single String key exceeds 10 KB, or if the size of all elements of a key combined exceeds 50 MB, the key is defined as a big key.
Keys that have a large number of elements. If the number of elements in a key exceeds 5000, the key is defined as a big key.
Hot key
A key is defined as a hot key if it is frequently requested or if it occupies a large number of resources. For example:
In a cluster instance, a shard processes 10,000 requests per second, among which 3000 are performed on the same key.
In a cluster instance, a shard uses a total of 100 Mbits/s inbound and outbound bandwidth, among which 80 Mbits/s is used by the HGETALL operation on a Hash key.