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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #789: DRILL-5356: Refactor Parquet Record Reader
Date Sun, 19 Mar 2017 19:53:37 GMT
GitHub user paul-rogers opened a pull request:

    https://github.com/apache/drill/pull/789

    DRILL-5356: Refactor Parquet Record Reader

    The Parquet reader is Drill's premier data source and has worked very well
    for many years. As with any piece of code, it has grown in complexity over
    that time and has become hard to understand and maintain.
    
    In work in another project, we found that Parquet is accidentally creating
    "low density" batches: record batches with little actual data compared to
    the amount of memory allocated. We'd like to fix that.
    
    However, the current complexity of the reader code creates a barrier to
    making improvements: the code is so complex that it is often better to
    leave bugs unfixed, or risk spending large amounts of time struggling to
    make small changes.
    
    This commit offers to help revitalize the Parquet reader. Functionality is
    identical to the code in master; but code has been pulled apart into
    various classes each of which focuses on one part of the task: building
    up a schema, keeping track of read state, a strategy for reading various
    combinations of records, etc. The idea is that it is easier to understand
    several small, focused classes than one huge, complex class. Indeed, the
    idea of small, focused classes is common in the industry; it is nothing new.
    
    Unit tests pass with the change. Since no logic has chanaged, we only moved
    lines of code, that is a good indication that everything still works.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/paul-rogers/drill DRILL-5356

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/drill/pull/789.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #789
    
----
commit f54fc657ef4bda5db2743032ab64b504183f93c8
Author: Paul Rogers <progers@maprtech.com>
Date:   2017-03-15T20:49:07Z

    DRILL-5356: Refactor Parquet Record Reader
    
    The Parquet reader is Drill's premier data source and has worked very well
    for many years. As with any piece of code, it has grown in complexity over
    that time and has become hard to understand and maintain.
    
    In work in another project, we found that Parquet is accidentally creating
    "low density" batches: record batches with little actual data compared to
    the amount of memory allocated. We'd like to fix that.
    
    However, the current complexity of the reader code creates a barrier to
    making improvements: the code is so complex that it is often better to
    leave bugs unfixed, or risk spending large amounts of time struggling to
    make small changes.
    
    This commit offers to help revitalize the Parquet reader. Functionality is
    identical to the code in master; but code has been pulled apart into
    various classes each of which focuses on one part of the task: building
    up a schema, keeping track of read state, a strategy for reading various
    combinations of records, etc. The idea is that it is easier to understand
    several small, focused classes than one huge, complex class. Indeed, the
    idea of small, focused classes is common in the industry; it is nothing new.
    
    Unit tests pass with the change. Since no logic has chanaged, we only moved
    lines of code, that is a good indication that everything still works.

----


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