Hey everyone, TL;DR Adding classic DB constraints as a system level coprocessor to help simplify using HBase and ease adopting.
Coprocessors are a really powerful mechanism and are incredibly useful for a variety of things. However, I feel like the mechanism for using them can be very daunting and, for certain features, could do with some simplification. What I would like to propose is a simple interface that people can use to implement a 'constraint' (matching the classic database definition). This would help ease of adoption by helping HBase more easily check that box, help minimize code duplication across organizations, and lead to easier adoption. Essentially, people would implement a 'Constraint' interface for checking keys before they are put into a table. Puts that are valid get written to the table, but if not people can will throw an exception that gets propagated back to the client explaining why the put was invalid. Constraints would be set on a per-table basis and the user would be expected to ensure the jars containing the constraint are present on the machines serving that table. Yes, people could roll their own mechanism for doing this via coprocessors each time, but this would make it easier to do so, so you only have to implement a very minimal interface and not worry about the specifics. If people are interested, I would like to open a Jira on the feature. I've got a basic implementation, but would like to expand it to be a more integrated, top-level element of the code. I just don't want to waste my time doing a full blown impl and then not have at least general concensus on it being a good feature. One of the complaints I commonly hear about HBase is that, to outsiders, it is difficult to figure out and use (though once you do, its solid). This would be a step to make it easier to use and adopt. Thanks, Jesse Yates
