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From "Cheolsoo Park (JIRA)" <j...@apache.org>
Subject [jira] [Created] (PIG-3645) Replace Random with UUID in FileLocalizer.getTemporaryPath()
Date Fri, 27 Dec 2013 19:53:50 GMT
Cheolsoo Park created PIG-3645:
----------------------------------

             Summary: Replace Random with UUID in FileLocalizer.getTemporaryPath()
                 Key: PIG-3645
                 URL: https://issues.apache.org/jira/browse/PIG-3645
             Project: Pig
          Issue Type: Improvement
          Components: impl
            Reporter: Cheolsoo Park
            Assignee: Cheolsoo Park
            Priority: Minor
             Fix For: 0.13.0


Currently, temporary paths are generated by FileLocalizer using Random.nextInt(). To provide
strong randomness, MapReduceLauncher resets the Random object every time when compiling physical
plan to MR plan:
{code}
MRCompiler comp = new MRCompiler(php, pc); 
comp.randomizeFileLocalizer(); // This in turn calls FileLocalizer.setR(new Random()).
{code}

Besides, there are a couple of places calling FileLocalizer.setR() (e.g. MRCompiler) with
some random seed.

I think-
# Randomizing Random seed is unnecessary if we switch to UUID.
# Setting Random objects in code like this is error-prone because it can be easily broken
by having or missing a FileLocalizer.setR() somewhere else. See an example [here|http://search-hadoop.com/m/2nxTzQXfHw1].

So I propose that we remove all this "randomizing Random seed" code and use UUID instead in
temporary paths.

For unit tests that compare the results against gold files, we should still allow to set Random
seed through FileLocalizer.setR(). But this method will be annotated as "VisibleForTesting"
to ensure it is not used nowhere else other than in unit tests.

Regarding the existing gold files, they can be easily regenerated by TestMRCompiler as follows-
{code}
FileOutputStream fos = new FileOutputStream(expectedFile + "_new");
PrintWriter pw = new PrintWriter(fos);
pw.write(compiledPlan);
{code}

I assume there won't be any kind of regressions due to this change. But please let me know
if I am wrong.



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