What is a database cluster?

Question

Database

I read it on the Internet, it seems clear, but I can’t finally explain to myself (
Can someone tell on your fingers what a cluster is (and not only for databases), clustering, etc.
Thank you

Answer 1

Clustering, in simple words, is a division into groups, according to certain criteria. A cluster is a group of objects.

Answer 2

I’ll try to explain on my fingers
In most cases, the main load goes to reading the database, it often happens that one machine cannot cope with the existing load, then they raise the cluster - they run the DBMS on several machines, one of them is declared the master, the rest of the replicas
The master only deals with recording and distribution ready changes by replicas
A we read only from replicas, balancing the load between them, thereby reducing the load on each of them and reducing the response time