[jira] [Commented] (ORC-595) Optimize Decimal64 scale calculation

["Panagiotis Garefalakis (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ORC-595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17036331#comment-17036331 ] 

Panagiotis Garefalakis commented on ORC-595:
--------------------------------------------

Patch is now available in the PR, also run DecimalBench for comparison (check attachments):


{code:java}
DecimalBench.read USE_DECIMAL64 avgt(5) 6428361.744 us/op (original)
     vs
DecimalBench.read USE_DECIMAL64 avgt(5) 5846104.832 us/op (ORC-595){code}

[~rameshkumar] [~gopalv] can you please take a look?

> Optimize Decimal64 scale calculation
> ------------------------------------
>
>                 Key: ORC-595
>                 URL: https://issues.apache.org/jira/browse/ORC-595
>             Project: ORC
>          Issue Type: Improvement
>          Components: encoding
>            Reporter: Panagiotis Garefalakis
>            Assignee: Panagiotis Garefalakis
>            Priority: Critical
>         Attachments: DecimalBench-Clean-scale2.log, DecimalBench-ORC-595-scale2.log
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> Currently Decimal64 is using an inner loop to apply the correct scale to each read Long value [https://github.com/apache/orc/blob/master/java/core/src/java/org/apache/orc/impl/TreeReaderFactory.java#L1294]
> A more efficient way would be to apply the scale using a single array access and by multiplying by 10 in the power of (scale - scratchScaleVector[r]).
> An extra optimization would be to keep all powers of 10 (up to 18) in a static array and reuse it across runtime instead of calculating each time.
> cc: [~rameshkumar] [~gopalv]



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