just for completeness, this issue is tracked with https://issues.apache.org/jira/browse/SYSTEMML-635 and the fix will be available tomorrow.

Regards,
Matthias

Inactive hide details for Matthias Boehm---04/14/2016 07:53:43 PM---Hi Ethan, thanks for catching this issue. The parfor scriptMatthias Boehm---04/14/2016 07:53:43 PM---Hi Ethan, thanks for catching this issue. The parfor script itself is perfectly fine

From: Matthias Boehm/Almaden/IBM@IBMUS
To: dev@systemml.incubator.apache.org
Cc: "Ethan Xu" <ethan.yifanxu@gmail.com>
Date: 04/14/2016 07:53 PM
Subject: Re: parfor fails





Hi Ethan,

thanks for catching this issue. The parfor script itself is perfectly fine but you encountered an interesting runtime bug. Usually, you can find the actual cause at the bottom of the stacktrace or in previous exceptions. I was able to reproduce this issue if NO systemml config file is provided (fails on parsing this non-existing config in the parfor mr job task setup). So the workaround is to put a SystemML-config.xml into the same directory. Interestingly, the issue did not show up in our testsuite because we always specify a default configuration there (which was until recently mandatory).

As a side note, we strongly recommend parfor over for loops here because it runs the entire loop in 1 instead of 2396 MR jobs due to automatic data partitioning. However, for the specific example at hand, a data-parallel formulation (with "
s = colSums(x==0)") would be even better as it allows for partial aggregation and hence reduces shuffle.

Regards,
Matthias

Ethan Xu ---04/14/2016 01:34:24 PM---Hello, I have a quick question. The following script fails with this error:

From:
Ethan Xu <ethan.yifanxu@gmail.com>
To:
dev@systemml.incubator.apache.org
Date:
04/14/2016 01:34 PM
Subject:
parfor fails




Hello,

I have a quick question. The following script fails with this error:

org.apache.sysml.runtime.DMLRuntimeException: PARFOR: Failed to execute
loop in parallel.

Here is the dml script:

x=read($X);

print("number of rows of x = " + nrow(x));
print("number of cols of x = " + ncol(x));

parfor(i in 1:ncol(x), check=0){
  a = x[,i];
  print("number of 0's in col " + i + " = " + sum(a == 0));
}

where X is a 35 million by 2396 matrix (coded and dummy coded numerical
matrix) on HDFS. The script runs fine with regular 'for' loops.

Could someone explain why this script cannot run in parallel? Was it a
wrong way to code parfor?

Thanks,

Ethan