Andrew McNabb wrote:
Does Hadoop run multiple threads on a single slave?
Yes, although each task runs in a separate JVM, not a thread. A slave will run up to mapred.tasktracker.tasks.maximum map and/or reduce tasks at a time.
I have mapred.map.tasks set to 7 (this should be enough to see two jobs on each client, though I plan on eventually setting it higher). mapred.tasktracker.tasks.maximum is 3 (eventually this will be higher, too).
The actual number of map tasks is determined by the number of input splits. Perhaps your input data is not big enough to result in more than a few input splits? A SequenceFile-format input cannot be split into chunks smaller than 2k bytes.
Doug
