[jira] [Created] (ARROW-3245) Infer index and/or filtering from parquet column statistics

["Martin Durant (JIRA)" <ji...@apache.org>]

Martin Durant created ARROW-3245:
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             Summary: Infer index and/or filtering from parquet column statistics
                 Key: ARROW-3245
                 URL: https://issues.apache.org/jira/browse/ARROW-3245
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Python
            Reporter: Martin Durant


The metadata included in parquet generally gives the min/max of data for each chunk of each column. This allows early filtering out of whole chunks if they do not meet some criterion, and can greatly reduce reading burden in some circumstances. In Dask, we care about this for setting an index and its "divisions" (start/stop values for each data partition) and for directly avoiding including some chunks in the graph of tasks to be processed. Similarly, filtering may be applied on the values of fields defined by the directory partitioning.

 

Currently, dask using the fastparquet backend is able to infer possible columns to use as an index, perform filtering on that index and do general filtering on any column which has statistical or partitioning information. It would be very helpful to have such facilities via pyarrow also.

 

(please forgive that some of this has already been mentioned elsewhere; this is one of the entries in the list at [https://github.com/dask/fastparquet/issues/374] as a feature that is useful in fastparquet)



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