Hi list, I am trying to run a Join query on my 10 node cluster. My query looks as follows
select * from A JOIN B on (A.a = B.b) size of A = 15 million rows size of B = 1 million rows The problem is A.a and B.b has around 25-30 distinct values per column which implies that they have high selectivities and the reducers are bulky. However the performance hit is so horrible that , ALL my reducers hang @ 75% for 6 hours and doesn't move further. The only thing that log shows up is "Join operator - forwarding rows ---------------<Huge number>" kinds of logs for all this long. What does this mean ? There is no swapping happening and the CPU % is constantly around 40% for all this time (observed through Ganglia) . Any way I can solve this problem? Can anyone help me with this? Thanks, jS
