We have a streaming application containing approximately 12 jobs every batch,
running in streaming mode (4 sec batches). Each job has several
transformations and 1 action (output to cassandra) which causes the
execution of the job (DAG)
For example the first job,
/job 1
---> receive Stream A --> map --> filter -> (union with another stream B)
--> map -->/ groupbykey --> transform --> reducebykey --> map
Likewise we go thro' few more transforms and save to database (job2,
job3...)
Recently we added a new transformation further downstream wherein we union
the output of DStream from job 1 (in italics) with output from a new
transformation(job 5). It appears the whole execution thus far is repeated
which is redundant (I can see this in execution graph & also performance ->
processing time).
That is, with this additional transformation (union with a stream processed
upstream) each batch runs as much as 2.5 times slower compared to runs
without the union. If I cache the DStream from job 1(italics), performance
improves substantially but hit out of memory errors within few hours.
What is the recommended way to cache/unpersist in such a scenario? there is
no dstream level "unpersist"
setting "spark.streaming.unpersist" to true and
streamingContext.remember("duration") did not help.
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