[jira] Commented: (LUCENE-892) CompoundFileReader's openInput produces streams that may do an extra buffer copy

["Razan Abbass (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-892?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12919671#action_12919671 ] 

Razan Abbass commented on LUCENE-892:
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> CompoundFileReader's openInput produces streams that may do an extra buffer copy
> --------------------------------------------------------------------------------
>
>                 Key: LUCENE-892
>                 URL: https://issues.apache.org/jira/browse/LUCENE-892
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.1
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.3
>
>         Attachments: LUCENE-892.patch
>
>
> Spinoff of LUCENE-888.
> The class for reading from a compound file (CompoundFileReader) has a
> primary stream which is a BufferedIndexInput when that stream is from
> an FSDirectory (which is the norm).  That is one layer of buffering.
> Then, when its openInput is called, a CSIndexInput is created which
> also subclasses from BufferedIndexInput.  That's a second layer of
> buffering.
> When a consumer actually uses that CSIndexInput to read, and a call to
> readByte or readBytes runs out of what's in the first buffer, it will
> go to refill its buffer.  But that refill calls the first
> BufferedIndexInput which in turn may refill its buffer (a double
> copy) by reading the underlying stream.
> Not sure how to fix it yet but we should change things to not do the
> extra buffer copy.

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