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From jatinganhotra <jatin.ganho...@gmail.com>
Subject How can I access data on RDDs?
Date Tue, 06 Oct 2015 06:58:23 GMT
Consider the following 2 scenarios:

*Scenario #1*
val pagecounts = sc.textFile("data/pagecounts")
pagecounts.checkpoint
pagecounts.count

*Scenario #2*
val pagecounts = sc.textFile("data/pagecounts")
pagecounts.count

The total time show in the Spark shell Application UI was different for both
scenarios. /Scenario #1 took 0.5 seconds, while scenario #2 took only 0.2
s/.

*Questions:*
1. I understand that scenario #1 is taking more time, because the RDD is
check-pointed (written to disk). Is there a way I can know the time taken
for checkpoint, from the total time?  

The Spark shell Application UI shows the following - Scheduler delay, Task
Deserialization time, GC time, Result serialization time, getting result
time. But, doesn't show the breakdown for checkpointing.  

2. Is there a way to access the above metrics e.g. scheduler delay, GC time
and save them programmatically? I want to log some of the above metrics for
every action invoked on an RDD.  

3. How can I programmatically access the following information:  
- Size of an RDD, when persisted to disk on checkpointing?  
- How much percentage of an RDD is in memory currently?  
- Overall time taken for computing an RDD?  

Please let me know if you need more information.



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