Greetings,

We've a fairly large dataset (around 60GB) to be loaded and crunched in
real time. The kind of data operations that will be performed on this data
are simple read only aggregates after filtering the data.table instance
based on the parameters that will passed in real time. We need to have more
than one instance of such R process running to serve different testing
environments (each testing environment has fairly identical dataset but do
have a *small amount of changes*). As we all know, data.table loads the
entire dataset into memory for processing and hence we are facing a
constraint on number of such process that we could run on the machine. On a
128GB RAM machine, we are coming up with ways in which we could reduce the
memory footprint so that we can try to spawn more instances and use the
resources efficiently. One of the approaches we tried out was memory
de-duplication using UKSM (
http://kerneldedup.org/en/projects/uksm/introduction), given that we did
have few idle cpu cores. Outcome of the experiment was quite impressive,
considering that the effort to set it up was quite less and the entire
approach considers the application layer as a black box.

Quick snapshot of the results:
1 Instance (without UKSM): ~60GB RAM was being used
1 Instance (with UKSM): ~53 GB RAM was being used

2 Instance (without UKSM): ~125GB RAM was being used
2 Instance (with UKSM): ~81 GB RAM was being used

We can see that around 44 GB of RAM was saved after UKSM merged similar
pages and all this for  a compromise of 1 CPU core on a 48 core machine. We
did not feel any noticeable degradation of performance because the data is
refreshed by a batch job only once (every morning); UKSM gets in at this
time and performs the same page merging and for the rest of day, its just
read only analysis. The kind of queries we fire on the dataset at most
scans 2-3GB of the entire dataset and hence the query subset spike was low
as well.

We're interested in knowing if this is a plausible solution to this
problem? Any other points/solutions that we should be considering?

-- 
Thanks,
M. Varadharajan

------------------------------------------------

"Experience is what you get when you didn't get what you wanted"
               -By Prof. Randy Pausch in "The Last Lecture"

My Journal :- www.thinkasgeek.wordpress.com

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