I am currently working to set up an OLAP data warehouse using Hive on top of Hadoop. We have a considerable amount of data that comes from the ad servers on which we need to perform various kinds of analysis.
Writing a map-reduce job is not difficult in principle – it's just time consuming and requires the skills of a trained java engineer, which wouldn't be needed were we using SQL. That's where hive comes in: it allows us to query an hadoop data store using a flavor of SQL.
