When creating custom Operations (Function
,
Filter
, Aggregator
, or
Buffer
) do not store operation state in class
fields.
For example, if implementing a custom "counter"
Aggregator
, do not create a field named "count"
and increment it on every
Aggregator.aggregate()
call. There is no
guarantee that your Operation will be called from a single thread in a
JVM - and future versions of Hadoop or Cascading local mode might
execute the same operation from multiple threads.
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