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Date: Sat, 9 Jul 2011 13:03:16 +0000 (UTC)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Created] (LUCENE-3297) FST doesn't fully share common
 prefix across all outputs
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FST doesn't fully share common prefix across all outputs
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                 Key: LUCENE-3297
                 URL: https://issues.apache.org/jira/browse/LUCENE-3297
             Project: Lucene - Java
          Issue Type: Improvement
            Reporter: Michael McCandless
            Priority: Minor


FST will try to share prefixes of outputs when possible, however in the [I think unusual in practice] case where all outputs share a common prefix, FST really ought to store this just once, on the root arc, but instead it's only able to push back to the N root arcs.  It's sort of an off-by-one on how far back the pushing goes...

One [synthetic] example where this makes a big difference is the new Test2BPostings test, when it uses MemoryCodec, because this test has 26 terms (letters of alphabet) and each term has exactly the same long (~85 MB) all 1s byte[] as the postings.  If we fixed this issue, then the resulting FST would only be ~85 MB but now instead it needs to be ~85 * 26 MB.

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