Piyush Narang created PARQUET-601:
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Summary: Add support in Parquet to configure the encoding used by
ValueWriters
Key: PARQUET-601
URL: https://issues.apache.org/jira/browse/PARQUET-601
Project: Parquet
Issue Type: Bug
Components: parquet-mr
Reporter: Piyush Narang
Assignee: Piyush Narang
Parquet is currently structured to choose the appropriate value writer based on
the type of the column as well as the Parquet version. Value writers are
responsible for writing out values with the appropriate encoding. As an
example, for Boolean data types, we use BooleanPlainValuesWriter (v1.0) or
RunLengthBitPackingHybridValuesWriter (v2.0). The code to take these decisions
is in
ParquetProperties(https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/column/ParquetProperties.java#L242).
Thanks to this set up, the writer(s) (and hence encoding) for each data type is
hard coded in the Parquet source code.
Would be nice to support being able to override the encodings per type via
config. That allows users to experiment with various encoding strategies
manually as well as enables them to override the hardcoded defaults if they
don't suit their use case.
We can override encodings per data type (int32 / int64 / ...).
Something on the lines of:
parquet.writer.encoding-override.<type> = "encoding1[,encoding2]"
As an example:
"parquet.writer.encoding-override.int32" = "plain"
(Chooses Plain encoding and hence the PlainValuesWriter).
When a primary + fallback need to be specified, we can do the following:
"parquet.writer.encoding-override.binary" = "rle_dictionary,delta_byte_array"
(Chooses RLE_DICTIONARY encoding as the initial encoding and DELTA_BYTE_ARRAY
encoding as the fallback and hence creates a
FallbackWriter(PlainBinaryDictionaryValuesWriter, DeltaByteArrayWriter).
In such cases we can mandate that the first encoding listed must allow for
Fallbacks by implementing
RequiresFallback(https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/column/values/RequiresFallback.java#L31).
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