Uploaded image for project: 'Lucene - Core'
  1. Lucene - Core
  2. LUCENE-705

CompoundFileWriter should pre-set its file length


    • Improvement
    • Status: Closed
    • Minor
    • Resolution: Fixed
    • 2.1
    • 2.4
    • core/index
    • None
    • New


      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


        1. LUCENE-705.patch
          3 kB
          Michael McCandless



            mikemccand Michael McCandless
            mikemccand Michael McCandless
            1 Vote for this issue
            0 Start watching this issue