[jira] [Commented] (PARQUET-601) Add support in Parquet to configure the encoding used by ValueWriters

["Takeshi Yamamuro (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PARQUET-601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15727804#comment-15727804 ] 

Takeshi Yamamuro commented on PARQUET-601:
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Hi, I have one question; I tried this new feature in v1.9 and could override ValuesWriterFactory via ParquetProperties though, I'm not sure how to define an new ValueReader for the new writer. IIUC I need to add a new entry in Encoding though,  it seems to be difficult to do that because ti's hard-coded. Anything I miss? Also, any document about how to define a new encoders?

> 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: Improvement
>          Components: parquet-mr
>            Reporter: Piyush Narang
>            Assignee: Piyush Narang
>             Fix For: format-2.4.0
>
>
> 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:
> {code}
> parquet.writer.encoding-override.<type> = "encoding1[,encoding2]"
> {code}
> As an example:
> {code}
> "parquet.writer.encoding-override.int32" = "plain"
> (Chooses Plain encoding and hence the PlainValuesWriter).
> {code}
> When a primary + fallback need to be specified, we can do the following:
> {code}
> "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). 
> {code}
> 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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