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Date: Thu, 21 May 2009 13:47:45 -0700 (PDT)
From: "Shai Erera (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Created: (LUCENE-1652) Enhancements to Scorers following the
 changes to DocIdSetIterator
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Enhancements to Scorers following the changes to DocIdSetIterator
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                 Key: LUCENE-1652
                 URL: https://issues.apache.org/jira/browse/LUCENE-1652
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Search
            Reporter: Shai Erera
             Fix For: 3.0


In LUCENE-1614, we changed the semantics of DocIdSetIterator's methods to return a sentinel NO_MORE_DOCS (= Integer.MAX_VALUE) when the iterator has exhausted. Due to backward compatibility issues, we couldn't implement that semantics in doc(). Therefore this issue, which can be introduced in 3.0 only will:
# Implement the new semantics in all extending classes, such that doc() will return NO_MORE_DOCS when the iterator has exhausted.
# Change BooleanScorer to take advantage of that by removing sub.done from SubScorer and operate under the assumption that NO_MORE_DOCS is larger than any doc ID (Integer.MAX_VALUE).
# Change ConjunctionScorer to operate under the same assumptions and remove 'more'.
# Change ReqExclScorer to not rely on reqScorer in doc(), since the latter may be null.
# Make more changes to ConjunctionScorer's init() and remove 'firstTime' to improve the performance of nextDoc(), score(), advance().
# Add start()/finish() to DISI?

A snippet from LUCENE-1614 regarding the change in BooleanScorer

{code}
int doc = sub.done ? -1 : scorer.doc();
while (!sub.done && doc < end) {
  sub.collector.collect(doc);
  doc = scorer.nextDoc();
  sub.done = doc < 0;
}
{code}

To this:

{code}
int doc = scorer.doc();
while (doc < end) {
  sub.collector.collect(doc);
  doc = scorer.nextDoc();
}
{code}

And in ConjunctionScorer, change this:

{code}
while (more && (firstScorer=scorers[first]).doc() < (lastDoc=lastScorer.doc())) {
  more = firstScorer.advance(lastDoc) >= 0;
  lastScorer = firstScorer;
  first = (first == (scorers.length-1)) ? 0 : first+1;
}
return more;
{code}

To this:

{code}
while ((firstScorer=scorers[first]).doc() < (lastDoc=lastScorer.doc())) {
  firstScorer.advance(lastDoc);
  lastScorer = firstScorer;
  first = (first == (scorers.length-1)) ? 0 : first+1;
}
return lastDoc != DOC_SENTINEL;
{code}

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