title: which determines the number of map tasks and reduce tasks in hive?
body: <p>I use hive to run a query "select * from T1,T2 where T1.a=T2.b", and the schema is T1(a int, b int),T2(a int,b int), when it runs, 6 map tasks and one reduce task generated, and I want to ask that, which determined the number of map tasks and reduce tasks? is the data volume?</p>