Here is the case: the first doc under pe is 100. - the first call advanceExact(10) returns false and pe is advanced to 100. - the second call advanceExact(20) returns false without attempting to advance pe, but just checking current doc. another edge case, when pe is exhausted and docId() returns NO_MORE_DOCS (Integer.MAX_VALUE), thus there will be no more attempts to advance it again.
On Sun, Jan 27, 2019 at 10:35 PM MarcoR <grumpyrodrig...@protonmail.com> wrote: > Hi, > > TermFreqDoubleValuesSource is used to expose a particular indexreader stat > as per https://issues.apache.org/jira/browse/LUCENE-7736 > > I noticed that the advanceExact method is checking for the condition in > which the postingsenum may have moved ahead of the doc Id of the > FilterScorer which calls advanceExact method (I'm referring to > implementation of FunctionScoreWeight.scorer method) > > The code I'm talking about is this: > > return new DoubleValues() { > @Override > public double doubleValue() throws IOException { > return pe.freq(); > } > > @Override > public boolean advanceExact(int doc) throws IOException { > if (pe.docID() > doc) > return false; > return pe.docID() == doc || pe.advance(doc) == doc; > } > }; > > What I'm curious about is why the check on pe.docId() is necessary? Given > the postings enum is created specifically for the purpose of building the > DoubleValues instance and its reference does not escape the parent > TermFreqDoubleValuesSource .getValues(..) method, how can it get ahead of > the scorer's docId? > I can imagine the scorer's doc id getting ahead of the postings enum since > the scorer my skip documents that does not fit some criteria but since > there > is nothing else that could be moving the postings enum ahead, why this > check? > > An obvious extension of the question is, why do we return false if the > checked condition is true? Is it really the case that DoubleValues cannot > be > provided if postingsEnum's docId is ahead? How do we safely assume that > this > is the case until scorer catches up with postings enum? > > I'm working on implementing some custom logic based on > TermFreqDoubleValuesSource and I would like to understand its mechanics > properly. > > > > -- > Sent from: > http://lucene.472066.n3.nabble.com/Lucene-Java-Developer-f564358.html > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org > For additional commands, e-mail: dev-h...@lucene.apache.org > > -- Sincerely yours Mikhail Khludnev
