What is CQRS?
Greg says what it’s not, and since he didn’t use the opportunity to also succinctly express what it is, I helped him out in the comments:
CQRS ("Command-Query Responsibility Segregation") is a simple pattern that strictly segregates the responsibility of handling command input into an autonomous system from the responsibility of handling side-effect-free query/read access on the same system. Consequently, the decoupling allows for any number of homogeneous or heterogeneous query/read modules...