[jira] [Commented] (LUCENE-9480) investigate slow DataInput.skipBytes

["Adrien Grand (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-9480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17183764#comment-17183764 ] 

Adrien Grand commented on LUCENE-9480:
--------------------------------------

Options 1 and 2 are lower hanging fruits, but collapsing DataInput and IndexInput is the most appealing to me. I've been bitten a couple times by APIs that took IndexInputs and not being able to pass them a DataInput even though these are essentially the same thing.

> investigate slow DataInput.skipBytes
> ------------------------------------
>
>                 Key: LUCENE-9480
>                 URL: https://issues.apache.org/jira/browse/LUCENE-9480
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Robert Muir
>            Priority: Major
>
> Currently DataInput has skipBytes(), but IndexInput also adds seek(). 
> There isn't a clear reason about the differences in the two methods: why would you choose one over the other?
> It causes some performance issues: for example the default implementation actually reads bytes into a byte array and throws everything away. This is really silly for MMapDirectory: skipping bytes should only be a glorified {{+=}}. 
> So when I look at latest LUCENE-9447 patch, I can't help but think a ton of waste is happening:
> * Maybe skipBytes() is only used because the stored fields compressor interface happens to take DataInput? Should it take IndexInput instead?
> * Should skipBytes() be overridden by MMapDirectory rather than delegating to super? doing real reads and byte array copies isn't free. It should be a {{+=}} with single bounds check.
> * Should we revisit having DataInput vs IndexInput at all? Maybe they should be collapsed into one thing?



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