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Date: Tue, 14 Jun 2011 00:12:47 +0000 (UTC)
From: "Robert Muir (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-3201) improved compound file handling
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    [ https://issues.apache.org/jira/browse/LUCENE-3201?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13048912#comment-13048912 ] 

Robert Muir commented on LUCENE-3201:
-------------------------------------

I think for this one, I prefer to wait for Uwe's refactoring of MMap on LUCENE-3200.
Then mmap is simpler, and i think we can even use the same indexinput implementation here.

This would mean no slowdown when searching CFS.


> improved compound file handling
> -------------------------------
>
>                 Key: LUCENE-3201
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3201
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Robert Muir
>
> Currently CompoundFileReader could use some improvements, i see the following problems
> * its CSIndexInput extends bufferedindexinput, which is stupid for directories like mmap.
> * it seeks on every readInternal
> * its not possible for a directory to override or improve the handling of compound files.
> for example: it seems if you were impl'ing this thing from scratch, you would just wrap the II directly (not extend BufferedIndexInput,
> and add compound file offset X to seek() calls, and override length(). But of course, then you couldnt throw read past EOF always when you should,
> as a user could read into the next file and be left unaware.
> however, some directories could handle this better. for example MMapDirectory could return an indexinput that simply mmaps the 'slice' of the CFS file.
> its underlying bytebuffer etc naturally does bounds checks already etc, so it wouldnt need to be buffered, not even needing to add any offsets to seek(),
> as its position would just work.
> So I think we should try to refactor this so that a Directory can customize how compound files are handled, the simplest 
> case for the least code change would be to add this to Directory.java:
> {code}
>   public Directory openCompoundInput(String filename) {
>     return new CompoundFileReader(this, filename);
>   }
> {code}
> Because most code depends upon the fact compound files are implemented as a Directory and transparent. at least then a subclass could override...
> but the 'recursion' is a little ugly... we could still label it expert+internal+experimental or whatever.

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