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From Gylfi <gy...@berkeley.edu>
Subject Re: Using reference for RDD is safe?
Date Sat, 18 Jul 2015 08:12:53 GMT
Hi. 

"All transformations in Spark are lazy, in that they do not compute their
results right away. Instead, they just remember the transformations applied
to some base dataset (e.g. a file). The transformations are only computed
when an action requires a result to be returned to the driver program. This
design enables Spark to run more efficiently – for example, we can realize
that a dataset created through map will be used in a reduce and return only
the result of the reduce to the driver, rather than the larger mapped
dataset."
See section "RDD Operations" in
https://spark.apache.org/docs/1.2.0/programming-guide.html

Thus, neither your myrdd2 nor myrdd will exist until you call the count. 
What is stored is just "how to create myrdd and myrdd2" so yes, this is
safe.. 

When you run myrdd2.count the both RDDs are created, myrdd2 is counted and
the count printed out.
After the operation both RDDs are "destroyed" again. 
If you run the myrdd2.count again, both myrdd and myrdd2 are created again
.. 

If your transformation is expensive, you may want to keep the data around
and for that must use .persist() or .cache() etc.  

Regards,
   Gylfi. 




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