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From Matthias Boehm <mboe...@googlemail.com>
Subject Re: [HELP] Undesired Benchmark Results
Date Fri, 24 Mar 2017 04:55:03 GMT
thanks for the feedback Mingyang. Let me quickly explain what happens here
and subsequently give you a couple of workarounds.

1. Understanding the Bottleneck: For any text inputs, we will initially
compile distributed reblock operations that convert the text representation
into RDDs of matrix indexes and matrix blocks. At runtime, however,
SystemML decides to perform these conversions via a simple multi-threaded
read into memory if the data comfortably fits in the memory budget of the
driver (70% of max heap, i.e., 14GB in your case) and certain other
constraints are met. After the read, the in-memory matrix is handed over to
the buffer pool (15% of max heap), and if it doesn't fit, it's written to a
local cache directory, which is likely the reason for the performance issue
you encountered. You can verify this by looking at the "-stats" output,
which includes the cache statistics,

Cache hits (Mem, WB, FS, HDFS):    1717/0/0/2.
Cache writes (WB, FS, HDFS):    573/0/1.
Cache times (ACQr/m, RLS, EXP):    9.799/0.005/0.106/0.250 sec

where ACQ stands for 'acquire read' which includes RDD collects and local
reads, and RLS stands for 'release' which includes evictions to local disk.

2. Workarounds:
a) Binary data: In case of binary input data, you would likely not
encounter this issue, because we would not evict read binary matrices since
they can be recovered from HDFS at any time. You could explicitly convert
the input data to its binary representation via a simple read - write
script (with format="binary"). From a benchmark perspective, this would be
the preferable option anyway, unless to want to benchmark the data
ingestion part form external formats.

b) Smaller Memory budget: Since all decisions on local vs distributed
operations respect available memory constraints, you can influence these
decisions by (1) a smaller driver memory to force more operations to
distribute execution, or (2) a larger driver memory, to make the buffer
pool large enough to avoid evictions.

c) Forced execution type: You can also force all operations - independent
of the driver memory budget - to distributed operations by putting "-exec
spark" into your command line invocation. From a benchmark perspective, I
would however, not recommend this.

Thanks again for the feedback. While writing this comment, I actually came
to the conclusion that we could handle even the case with input csv better
in order to avoid evictions in these scenarios.


Regards,
Matthias



On Thu, Mar 23, 2017 at 8:41 PM, Mingyang Wang <miw092@eng.ucsd.edu> wrote:

> Hi Everyone,
>
> I got some some undesired results when running some benchmarks with
> SystemML, and I really hope to get some helps from you guys.
>
> Say, I want to read a large matrix in csv and retrieve the first cell with
> script
>
> # simple_read.dml
> data = read($RS)
> print("One Cell data[1,1]: " + toString(data[1,1]))
>
> and run it with the configuration such as
>
> spark-submit \
>     --driver-memory 20G \
>     --executor-memory 100G \
>     --executor-cores 20 \
>     --num-executors 1 \
>     --conf spark.driver.maxResultSize=0 \
>     --conf spark.rpc.message.maxSize=128 \
>     $SYSTEMML_HOME/target/SystemML.jar \
>     -f simple_read.dml \
>     -stats \
>     -explain \
>     -nvargs
> RS=/oasis/scratch/comet/hyoung/temp_project/scatter_
> data/TR20_FR4.00/RS_join.csv
>
> When the input matrix is 2x10^7 by 103 (around 20GB), things worked fine,
> as sp_rangeReIndex took 19.725s and sp_csvrblk took 11.330s. But when the
> input matrix is reduced to 10^7 by 103 (around 10GB), interesting things
> happened, as rangeReIndex took 92.024s and sp_csvrblk took 7.774s.
>
> These results were obtained with SystemML v0.13.0 on Spark 2.1.0 in
> standalone mode with 128GB memory and 24 cores.
>
> From the log, it seems that for the latter case, the control program in the
> driver took the main job and led to lots of disk I/O, thus the whole
> program had been slowed down.
>
> I understand that assigning the control program some tasks is a key
> component in SystemML. But this feature really brings in some chaos to the
> benchmarks in my case. Any suggestion about how to choose a better
> configuration or make some detours so I can obtain fair benchmarks on a
> wide range of data dimensions?
>
> If needed, I can attach the logs.
>
> I really appreciate your help!
>
>
> Regards,
> Mingyang Wang
> Graduate Student in UCSD CSE Dept.
>

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