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Is parquet using delta encoding for positions? #1552

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jpdna opened this Issue May 30, 2017 · 2 comments

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jpdna commented May 30, 2017

I'm having trouble confirming as parquet-tools is not building for me right now, but I wanted to check if we think that our long genomic positions are being encoded in the most efficient way possible (probably delta for sorted data) in parquet. See discussion here: https://issues.apache.org/jira/browse/PARQUET-225

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fnothaft May 30, 2017

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To get delta encoding, you need to set disableDictionaryEncoding to true. This effectively enables the Parquet 2 format, which supports delta encoding. There was a discussion recently on the Spark lists that the vectorized Spark SQL reader only supports Parquet 1, so you may see worse performance with delta encoding from Spark SQL. Truth be told, I looked at file sizes a while back and moving to delta encoding didn't seem to make a huge difference.

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fnothaft commented May 30, 2017

To get delta encoding, you need to set disableDictionaryEncoding to true. This effectively enables the Parquet 2 format, which supports delta encoding. There was a discussion recently on the Spark lists that the vectorized Spark SQL reader only supports Parquet 1, so you may see worse performance with delta encoding from Spark SQL. Truth be told, I looked at file sizes a while back and moving to delta encoding didn't seem to make a huge difference.

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fnothaft Jun 22, 2017

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I don't think there's anything actionable here for right now, so I'll close this. Please reopen if you have a question @jpdna.

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fnothaft commented Jun 22, 2017

I don't think there's anything actionable here for right now, so I'll close this. Please reopen if you have a question @jpdna.

@fnothaft fnothaft closed this Jun 22, 2017

@heuermh heuermh modified the milestone: 0.23.0 Jul 22, 2017

@heuermh heuermh added this to Completed in Release 0.23.0 Jan 4, 2018

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