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From "Imran Rashid (JIRA)" <>
Subject [jira] [Commented] (SPARK-9850) Adaptive execution in Spark
Date Mon, 24 Aug 2015 17:05:46 GMT


Imran Rashid commented on SPARK-9850:

I know the 1000 partitions used in the design doc is just for an example, but I just wanted
to point out that the number probably needs to be much larger.  With a 2GB limit per partition,
that is already 2 TB max.  My rule of thumb has been to keep partitions around 100 MB, which
is roughly inline with the 64 MB you mention in the doc, which brings you down to 100 GB.
 And given that you want to deal w/ skewed data etc., you probably actually want to leave
quite a bit of room, which limits you to relatively small datasets.

The key point is that after you go over 2000 partitions, you are going into {{HighlyCompressedMapOutput}}
territory, which will be relatively useless for this.  Perhaps each shuffle map task can always
send an uncompressed map status back to the driver?  Maybe you could only use the {{HighlyCompressedMapStatus}}
on the shuffle-read side?? I'm not sure about the performance implications, just throwing
out an idea.

> Adaptive execution in Spark
> ---------------------------
>                 Key: SPARK-9850
>                 URL:
>             Project: Spark
>          Issue Type: Epic
>          Components: Spark Core, SQL
>            Reporter: Matei Zaharia
>            Assignee: Yin Huai
>         Attachments: AdaptiveExecutionInSpark.pdf
> Query planning is one of the main factors in high performance, but the current Spark
engine requires the execution DAG for a job to be set in advance. Even with cost­-based optimization,
it is hard to know the behavior of data and user-defined functions well enough to always get
great execution plans. This JIRA proposes to add adaptive query execution, so that the engine
can change the plan for each query as it sees what data earlier stages produced.
> We propose adding this to Spark SQL / DataFrames first, using a new API in the Spark
engine that lets libraries run DAGs adaptively. In future JIRAs, the functionality could be
extended to other libraries or the RDD API, but that is more difficult than adding it in SQL.
> I've attached a design doc by Yin Huai and myself explaining how it would work in more

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