The Java client currently has an option to ignore duplicate row key errors, which is implemented by filtering the errors on the client side. If we are going to continue to support this feature (and the consensus seems to be that we probably should), we should promote it to a first class operation type that is handled on the server side. This would have a modest perf. improvement since less errors are returned, and it would allow INSERT IGNORE ops to be mixed in the same batch as other INSERT, DELETE, UPSERT, etc. ops.