something about cap

The short summary of the article is that CAP isn’t “C, A, or P, choose
two,” but rather “When P happens, choose A or C.”

Partitions, like death and taxes, are unavoidable – think of machine
death as just a partition of that machine out into the networking
equivalent of the afterlife. So it’s up to the system designer to
decide if, when that happens, we give up availability or give up
consistency.

In HBase’s case we choose consistency, so we have to give up some availability.
In Cassandra's case we choose availability.