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https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12713048#action_12713048
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Shai Erera commented on LUCENE-1614:
------------------------------------
About ConjunctionScorer.doNext() (this also applies to
FilteredQuery.advanceToCommon()). I've changed it, following Mike's proposal to
this:
{code}
private boolean doNext() throws IOException {
int first = 0;
lastDoc = scorers[scorers.length - 1].docID();
Scorer firstScorer;
while ((firstScorer = scorers[first]).docID() < lastDoc) {
lastDoc = firstScorer.advance(lastDoc);
first = first == scorers.length - 1 ? 0 : first + 1;
}
return lastDoc != NO_MORE_DOCS;
}
{code}
This indeed gets rid of 'more', the check for 'more' in the while condition and
also the assignment to more. But now I think it may introduce a different
inefficiency. Let's say that firstScorer.advance() returns NO_MORE_DOCS. The
next scorer's docID is obviously smaller, and therefore the following call will
be (first line in the 'while' body): *lastDoc =
firstScorer.advance(Integer.MAX_VALUE);*. There are Scorers which cannot
implement that efficiently.
With 'more' this would not have happened, since the while condition would
terminate before that.
Are we sure that that's a worthwhile enhancement.
BTW, the code for FilteredQuery looks like this:
{code}
while (scorerDoc != disiDoc) {
if (scorerDoc < disiDoc) {
if ((scorerDoc = scorer.advance(disiDoc)) == NO_MORE_DOCS) {
return NO_MORE_DOCS;
}
} else {
if ((disiDoc = docIdSetIterator.advance(scorerDoc)) ==
NO_MORE_DOCS) {
return NO_MORE_DOCS;
}
}
}
return scorerDoc;
{code}
And I thought to change it to this:
{code}
while (scorerDoc != disiDoc) {
if (scorerDoc < disiDoc) {
scorerDoc = scorer.advance(disiDoc);
} else {
disiDoc = docIdSetIterator.advance(scorerDoc);
}
}
return scorerDoc;
{code}
What do you think?
> Add next() and skipTo() variants to DocIdSetIterator that return the current
> doc, instead of boolean
> ----------------------------------------------------------------------------------------------------
>
> Key: LUCENE-1614
> URL: https://issues.apache.org/jira/browse/LUCENE-1614
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Shai Erera
> Fix For: 2.9
>
> Attachments: LUCENE-1614.patch, LUCENE-1614.patch, LUCENE-1614.patch
>
>
> See
> http://www.nabble.com/Another-possible-optimization---now-in-DocIdSetIterator-p23223319.html
> for the full discussion. The basic idea is to add variants to those two
> methods that return the current doc they are at, to save successive calls to
> doc(). If there are no more docs, return -1. A summary of what was discussed
> so far:
> # Deprecate those two methods.
> # Add nextDoc() and skipToDoc(int) that return doc, with default impl in DISI
> (calls next() and skipTo() respectively, and will be changed to abstract in
> 3.0).
> #* I actually would like to propose an alternative to the names: advance()
> and advance(int) - the first advances by one, the second advances to target.
> # Wherever these are used, do something like '(doc = advance()) >= 0' instead
> of comparing to -1 for improved performance.
> I will post a patch shortly
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