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From Aaron Davidson <ilike...@gmail.com>
Subject Re: [Performance] Possible regression in rdd.take()?
Date Thu, 19 Feb 2015 01:25:29 GMT
You might be seeing the result of this patch:

https://github.com/apache/spark/commit/d069c5d9d2f6ce06389ca2ddf0b3ae4db72c5797

which was introduced in 1.1.1. This patch disabled the ability for take()
to run without launching a Spark job, which means that the latency is
significantly increased for small jobs (but not for large ones). You can
try enabling local execution and seeing if your problem goes away.

On Wed, Feb 18, 2015 at 5:10 PM, Matt Cheah <mcheah@palantir.com> wrote:

> I actually tested Spark 1.2.0 with the code in the rdd.take() method
> swapped out for what was in Spark 1.0.2. The run time was still slower,
> which indicates to me something at work lower in the stack.
>
> -Matt Cheah
>
> On 2/18/15, 4:54 PM, "Patrick Wendell" <pwendell@gmail.com> wrote:
>
> >I believe the heuristic governing the way that take() decides to fetch
> >partitions changed between these versions. It could be that in certain
> >cases the new heuristic is worse, but it might be good to just look at
> >the source code and see, for your number of elements taken and number
> >of partitions, if there was any effective change in how aggressively
> >spark fetched partitions.
> >
> >This was quite a while ago, but I think the change was made because in
> >many cases the newer code works more efficiently.
> >
> >- Patrick
> >
> >On Wed, Feb 18, 2015 at 4:47 PM, Matt Cheah <mcheah@palantir.com> wrote:
> >> Hi everyone,
> >>
> >> Between Spark 1.0.2 and Spark 1.1.1, I have noticed that rdd.take()
> >> consistently has a slower execution time on the later release. I was
> >> wondering if anyone else has had similar observations.
> >>
> >> I have two setups where this reproduces. The first is a local test. I
> >> launched a spark cluster with 4 worker JVMs on my Mac, and launched a
> >> Spark-Shell. I retrieved the text file and immediately called
> >>rdd.take(N) on
> >> it, where N varied. The RDD is a plaintext CSV, 4GB in size, split over
> >>8
> >> files, which ends up having 128 partitions, and a total of 80000000
> >>rows.
> >> The numbers I discovered between Spark 1.0.2 and Spark 1.1.1 are, with
> >>all
> >> numbers being in seconds:
> >>
> >> 10000 items
> >>
> >> Spark 1.0.2: 0.069281, 0.012261, 0.011083
> >>
> >> Spark 1.1.1: 0.11577, 0.097636, 0.11321
> >>
> >>
> >> 40000 items
> >>
> >> Spark 1.0.2: 0.023751, 0.069365, 0.023603
> >>
> >> Spark 1.1.1: 0.224287, 0.229651, 0.158431
> >>
> >>
> >> 100000 items
> >>
> >> Spark 1.0.2: 0.047019, 0.049056, 0.042568
> >>
> >> Spark 1.1.1: 0.353277, 0.288965, 0.281751
> >>
> >>
> >> 400000 items
> >>
> >> Spark 1.0.2: 0.216048, 0.198049, 0.796037
> >>
> >> Spark 1.1.1: 1.865622, 2.224424, 2.037672
> >>
> >> This small test suite indicates a consistently reproducible performance
> >> regression.
> >>
> >>
> >> I also notice this on a larger scale test. The cluster used is on EC2:
> >>
> >> ec2 instance type: m2.4xlarge
> >> 10 slaves, 1 master
> >> ephemeral storage
> >> 70 cores, 50 GB/box
> >>
> >> In this case, I have a 100GB dataset split into 78 files totally 350
> >>million
> >> items, and I take the first 50,000 items from the RDD. In this case, I
> >>have
> >> tested this on different formats of the raw data.
> >>
> >> With plaintext files:
> >>
> >> Spark 1.0.2: 0.422s, 0.363s, 0.382s
> >>
> >> Spark 1.1.1: 4.54s, 1.28s, 1.221s, 1.13s
> >>
> >>
> >> With snappy-compressed Avro files:
> >>
> >> Spark 1.0.2: 0.73s, 0.395s, 0.426s
> >>
> >> Spark 1.1.1: 4.618s, 1.81s, 1.158s, 1.333s
> >>
> >> Again demonstrating a reproducible performance regression.
> >>
> >> I was wondering if anyone else observed this regression, and if so, if
> >> anyone would have any idea what could possibly have caused it between
> >>Spark
> >> 1.0.2 and Spark 1.1.1?
> >>
> >> Thanks,
> >>
> >> -Matt Cheah
>

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