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https://issues.apache.org/jira/browse/LUCENE-9480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17287433#comment-17287433
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Greg Miller commented on LUCENE-9480:
-------------------------------------
I've just attached a patch with a minimal improvement that implements a more
efficient #skipBytes in IndexInput while leaving other subclasses largely be.
The following places look like they could also be optimized. I'll likely follow
up with a change for these, but wanted to focus on this minimal version first
(maybe another Jira to track the additional opportunity?):
CompressingStoredFieldsReader, ByteSliceReader, ByteBuffersDataInput,
InputStreamDataInput, PagedBytes.
This is my first attempt at a Lucene change, so I welcome all feedback, etc.
Thanks!
> 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
> Attachments: LUCENE-9480.patch
>
>
> 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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