[jira] Commented: (LUCENE-705) CompoundFileWriter should pre-set its file length

["Grant Ingersoll (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558406#action_12558406 ] 

Grant Ingersoll commented on LUCENE-705:
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This seems reasonable, although I am not an expert in low-level file system calls like this.  I guess for me the thing would be to find out if the major filesystems support it (Windows, OSX, Linux) and then perhaps we can deal w/ others from there as they arise (i.e. those that don't support it)

> 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
>
> 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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