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Re: Performance issue in Beam 2.4 onwards


Hi Vojta,

I fully agree, that's why it makes sense to wait Eugene's feedback.

I remember we had some performance regression on the direct runner
identified thanks to Nexmark, but it has been addressed by reverting a
change.

Good catch anyway !

Regards
JB

On 09/07/2018 17:20, Vojtech Janota wrote:
> Hi Reuven,
> 
> I'm not really complaining about DirectRunner. In fact it seems to me as
> if what previously was considered as part of the "expensive extra
> checks" done by the DirectRunner is now done within the
> beam-runners-core-java library. Considering that all objects involved
> are immutable (in our case at least) and simple assignment is
> sufficient, the serialization-deserialization really seems as unwanted
> and hugely expensive correctness check. If there was a problem with
> identity copy, wasn't DirectRunner supposed to reveal it? 
> 
> Regards,
> Vojta
> 
> On Mon, Jul 9, 2018 at 4:46 PM, Reuven Lax <relax@xxxxxxxxxx
> <mailto:relax@xxxxxxxxxx>> wrote:
> 
>     Hi Vojita,
> 
>     One problem is that the DirectRunner is designed for testing, not
>     for performance. The DirectRunner currently does many
>     purposely-inefficient things, the point of which is to better expose
>     potential bugs in tests. For example, the DirectRunner will randomly
>     shuffle the order of PCollections to ensure that your code does not
>     rely on ordering.  All of this adds cost, because the current runner
>     is designed for testing. There have been requests in the past for an
>     "optimized" local runner, however we don't currently have such a thing.
> 
>     In this case, using coders to clone values is more correct. In a
>     distributed environment using encode/decode is the only way to copy
>     values, and the DirectRunner is trying to ensure that your code is
>     correct in a distributed environment.
> 
>     Reuven
> 
>     On Mon, Jul 9, 2018 at 7:22 AM Vojtech Janota
>     <vojta.janota@xxxxxxxxx <mailto:vojta.janota@xxxxxxxxx>> wrote:
> 
>         Hi,
> 
>         We are using Apache Beam in our project for some time now. Since
>         our datasets are of modest size, we have so far used
>         DirectRunner as the computation easily fits onto a single
>         machine. Recently we upgraded Beam from 2.2 to 2.4 and found out
>         that performance of our pipelines drastically deteriorated.
>         Pipelines that took ~3 minutes with 2.2 do not finish within
>         hours now. We tried to isolate the change that causes the
>         slowdown and came to the commits into the
>         "InMemoryStateInternals" class:
> 
>         * https://github.com/apache/beam/commit/32a427c
>         <https://github.com/apache/beam/commit/32a427c>
>         * https://github.com/apache/beam/commit/8151d82
>         <https://github.com/apache/beam/commit/8151d82>
> 
>         In a nutshell where previously the copy() method simply assigned:
> 
>           that.value = this.value
> 
>         There is now coder encode/decode combo hidden behind:
> 
>           that.value = uncheckedClone(coder, this.value)
> 
>         Can somebody explain the purpose of this change? Is it meant as
>         an additional "enforcement" point, similar to DirectRunner's
>         enforceImmutability and enforceEncodability? Or is it something
>         that is genuinely needed to provide correct behaviour of the
>         pipeline?
> 
>         Any hints or thoughts are appreciated.
> 
>         Regards,
>         Vojta
> 
>          
> 
> 
> 
> 

-- 
Jean-Baptiste Onofré
jbonofre@xxxxxxxxxx
http://blog.nanthrax.net
Talend - http://www.talend.com