Database Reference
In-Depth Information
Finally, note that the
Mapper
's
run()
method is public and may be customized by
users.
MultithreadedMapper
is an implementation that runs mappers concurrently
in a configurable number of threads (set by
mapre-
duce.mapper.multithreadedmapper.threads
). For most data processing
tasks, it confers no advantage over the default implementation. However, for mappers that
spend a long time processing each record — because they contact external servers, for ex-
ample — it allows multiple mappers to run in one JVM with little contention.
