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https://issues.apache.org/jira/browse/LUCENE-705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12564314#action_12564314
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Otis Gospodnetic commented on LUCENE-705:
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Didn't find time to comment on this earlier.
Does this mean one will no longer be able to tell exactly how large the index
really is (because some portion of some data files will actually be empty)?
> CompoundFileWriter should pre-set its file length
> -------------------------------------------------
>
> Key: LUCENE-705
> URL: https://issues.apache.org/jira/browse/LUCENE-705
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: 2.1
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 2.4
>
> Attachments: LUCENE-705.patch
>
>
> I've read that if you are writing a large file, it's best to pre-set
> the size of the file in advance before you write all of its contents.
> This in general minimizes fragmentation and improves IO performance
> against the file in the future.
> I think this makes sense (intuitively) but I haven't done any real
> performance testing to verify.
> Java has the java.io.File.setLength() method (since 1.2) for this.
> We can easily fix CompoundFileWriter to call setLength() on the file
> it's writing (and add setLength() method to IndexOutput). The
> CompoundFileWriter knows exactly how large its file will be.
> Another good thing is: if you are going run out of disk space, then,
> the setLength call should fail up front instead of failing when the
> compound file is actually written. This has two benefits: first, you
> find out sooner that you will run out of disk space, and, second, you
> don't fill up the disk down to 0 bytes left (always a frustrating
> experience!). Instead you leave what space was available
> and throw an IOException.
> My one hesitation here is: what if out there there exists a filesystem
> that can't handle this call, and it throws an IOException on that
> platform? But this is balanced against possible easy-win improvement
> in performance.
> Does anyone have any feedback / thoughts / experience relevant to
> this?
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