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https://issues.apache.org/jira/browse/PIG-3419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13744218#comment-13744218
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Cheolsoo Park commented on PIG-3419:
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[~achalsoni81], thank you very much for the great work! Although I am not a Pig
old-timer, I have been playing with your patch and have a few high-level
comments as follows:
# I love your ExecType interface. What I don't like is that there are two
things called ExecType:
{code}
org.apache.pig.ExecType
org.apache.pig.backend.executionengine.ExecType
{code}
Since you're introducing the ServiceLoader framework, the enum seems no longer
needed at all. Furthermore, eliminating it helps simplify the constructor code
of PigContext and PigServer.
# Currently, it is a bit hard to review your patch because there are too many
changes. To get it committed faster, I suggest we should avoid unnecessary
changes and minimize its scope. For example, having the PigServer constructor
signature unchanged helps avoid a lot of changes in Test*.java files.
# Julien already pointed out this in the RB, but your patch accidentally
reverts a couple of previous commits. I took them out.
I went ahead and made these changes myself -
[here|https://github.com/piaozhexiu/apache-pig/commit/9aee192116816ecf993d69a8c2f94abaff7f9739].
If everyone thinks this is a step forward, I will upload it in a new patch.
Please let me know.
> Pluggable Execution Engine
> ---------------------------
>
> Key: PIG-3419
> URL: https://issues.apache.org/jira/browse/PIG-3419
> Project: Pig
> Issue Type: New Feature
> Affects Versions: 0.12
> Reporter: Achal Soni
> Assignee: Achal Soni
> Priority: Minor
> Attachments: execengine.patch, mapreduce_execengine.patch,
> stats_scriptstate.patch, test_suite.patch
>
>
> In an effort to adapt Pig to work using Apache Tez
> (https://issues.apache.org/jira/browse/TEZ), I made some changes to allow for
> a cleaner ExecutionEngine abstraction than existed before. The changes are
> not that major as Pig was already relatively abstracted out between the
> frontend and backend. The changes in the attached commit are essentially the
> barebones changes -- I tried to not change the structure of Pig's different
> components too much. I think it will be interesting to see in the future how
> we can refactor more areas of Pig to really honor this abstraction between
> the frontend and backend.
> Some of the changes was to reinstate an ExecutionEngine interface to tie
> together the front end and backend, and making the changes in Pig to delegate
> to the EE when necessary, and creating an MRExecutionEngine that implements
> this interface. Other work included changing ExecType to cycle through the
> ExecutionEngines on the classpath and select the appropriate one (this is
> done using Java ServiceLoader, exactly how MapReduce does for choosing the
> framework to use between local and distributed mode). Also I tried to make
> ScriptState, JobStats, and PigStats as abstract as possible in its current
> state. I think in the future some work will need to be done here to perhaps
> re-evaluate the usage of ScriptState and the responsibilities of the
> different statistics classes. I haven't touched the PPNL, but I think more
> abstraction is needed here, perhaps in a separate patch.
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