Hive was invented by Facebook as a data warehouse layer on top of Hadoop, and has been adopted by HortonWorks. The benefit of Hive is that it enables programmers, with years of experience in relational databases, to write MapReduce jobs using SQL. The problem is that MapReduce is slow, and Hive slows it down even further.
HortonWorks is pushing for optimization (via project Stinger) of the developer friendly toolset provided by Hive. Cloudera has abandoned Hive in favor of Impala. Rather than translate SQL queries into MapReduce, Impala implements a massively parallel relational database on top of HDFS.