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From "Jason Altekruse (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-1950) Implement filter pushdown for Parquet
Date Wed, 07 Jan 2015 16:21:34 GMT
Jason Altekruse created DRILL-1950:
--------------------------------------

             Summary: Implement filter pushdown for Parquet
                 Key: DRILL-1950
                 URL: https://issues.apache.org/jira/browse/DRILL-1950
             Project: Apache Drill
          Issue Type: Improvement
            Reporter: Jason Altekruse
            Assignee: Jason Altekruse


The parquet reader currently supports project pushdown, for limiting the number of columns
read, however it does not use filter pushdown to read a subset of the requested columns. This
is particularly useful with parquet files that contain statistics, most importantly min and
max values on pages. Evaluating predicates against these values could save some major reading
and decoding time.

The largest barrier to implementing this is the current design of the reader. Firstly, we
currently have two separate parquet readers, one for reading flat files very quickly and another
or reading complex data. There are enhancements we can make the the flat reader, to make it
support nested data in a much more efficient manner. However the speed of the flat file reader
currently comes from being able to make vectorized copies out the the parquet file. This design
is somewhat at odds with filter pushdown, as we will only can make useful vectorized copies
if the filter matches a large run of values within the file. This might not be too rare a
case, assuming files are often somewhat sorted on a primary field like date or a numeric key,
and these are often fields used to limit the query to a subset of the data. However for cases
where we are filter out a few records here and there, we should just make individual copies.

We need to do more design work on the best way to balance performance with these use cases
in mind.



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