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From Li Li <>
Subject Re: why the of advance(int target) function of DocIdSetIterator is defined with uncertain?
Date Tue, 24 Apr 2012 02:56:10 GMT
I got it.
I found my test codes some problem.
the new test result is:
when minShould=1, new algorithm is a little bit faster than old one. when
minShould>1, old algorithm is faster.

On Sun, Apr 22, 2012 at 3:32 AM, Mikhail Khludnev <> wrote:

> Li,
> I can give you my understanding of difference in DisjunctionSumScorer and
> When you choose steady children approach, even you omit call score() you
> have to enumerate top of child scorers heap twice.
> Check nextDoc() from the patch: first loop pushes top of heap first, then
> the second loop through the top is done by
> countMatches(1); countMatches(2);
> Current DisjunctionSumScorer enumerate top of heap once per every doc:
> while it loops through top of heap it counts number of clauses matched;
> accumulate score; and pushes top children one step forward.
> what's minimumNrMatchers do you have? can you upload your test github?
> (mail list rips attachments off)
> On Thu, Apr 19, 2012 at 7:34 AM, Li Li <> wrote:
>> Michael McCandless wrote:
>> So... the good news is I made a new scorer (basically copied
>> DisjunctionMaxScorer and then tweaked from there) that scores the OR-only
>> case. All tests pass w/ this new scorer.
>> And more good news is that if you don't score (I sort by doctitle to do
>> that), you get a speedup – 7.7% in my simplistic test (prefix query unit*,
>> expands to 988 terms, but I force it to do a scoring BQ rewrite, plus force
>> it to use BS2 not BS – the nocommits in the patch).
>> But the bad news is with scoring on it's 22.7% slower!
>> And, the weird news is, I discovered accidentally that BS2 is much (> 2X)
>> faster for this one query. I think we need to modify the criteria that
>> decides whether to use BS or BS2... maybe when there are lots of
>> lowish-docFreq terms, BS2 is better?
>> ---------------
>> why new algorithm is 22% slower than old one?
>> I read the codes and feel them almost the same.
>> On Tue, Apr 17, 2012 at 8:16 PM, Mikhail Khludnev <
>>> wrote:
>>> Hello,
>>> I can't help with the particular question, but can share some
>>> experience. My task is roughly the same I've found the patch
>>> is absolutely useful
>>> (with one small addition, I'll post it in comments soon). By using it I
>>> have disjunction summing query with steady subscorers.
>>> Regards
>>> On Tue, Apr 17, 2012 at 2:37 PM, Li Li <> wrote:
>>>> hi all,
>>>>     I am now hacking the BooleanScorer2 to let it keep the docID() of
>>>> the leaf scorer(mostly possible TermScorer) the same as the top-level
>>>> Scorer. Why I want to do this is: When I Collect a doc, I want to know
>>>> which term is matched(especially for BooleanClause whose Occur is SHOULD).
>>>> we have discussed some solutions, such as adding bit masks in disjunction
>>>> scorers. with this method, when we finds a matched doc, we can recursively
>>>> find which leaf scorer is matched. But we think it's not very efficient and
>>>> not convenient to use(this is my proposal but not agreed by others in our
>>>> team). and then we came up with another one: Modifying DisjunctionSumScorer.
>>>>    we analysed the codes and found that the only Scorers used by
>>>> BooleanScorer2 that will make the children scorers' docID() not equal to
>>>> parent is an anonymous class inherited from DisjunctionSumScorer. All other
>>>> ones including SingleMatchScorer, countingConjunctionSumScorer(anonymous),
>>>> dualConjuctionSumScorer, ReqOptSumScorer and ReqExclScorer are fit our need.
>>>>    The implementation algorithm of DisjunctionSumScorer use a heap to
>>>> find the smallest doc. after finding a matched doc, the currentDoc is the
>>>> matched doc and all the scorers in the heap will call nextDoc() so all of
>>>> the scorers' current docID the nextDoc of currentDoc. if there are N level
>>>> DisjunctionSumScorer, the leaf scorer's current doc is the n-th next docId
>>>> of the root of the scorer tree.
>>>>    So we modify the DisjuctionSumScorer and let it behavior as we
>>>> expected. And then I wrote some TestCase and it works well. And also I
>>>> wrote some random generated TermScorer and compared the nextDoc(),score()
>>>> and advance(int) method of original DisjunctionSumScorer and modified one.
>>>> nextDoc() and score() and exactly the same. But for advance(int target),
>>>> found some interesting and strange things.
>>>>    at the beginning, I think if target is less than current docID, it
>>>> will just return current docID and do nothing. this assumption let my
>>>> algorithm go wrong. Then I read the codes of TermScorer and found each call
>>>> of advance(int) of TermScorer will call nextDoc() no matter whether current
>>>> docID is larger than target or not.
>>>>    So I am confused and then read the javadoc of DocIdSetIterator:
>>>> ----------------- javadoc of DocIdSetIterator.advance(int
>>>> target)-------------
>>>> int target)
>>>> throws IOException
>>>> Advances to the first beyond (see NOTE below) the current whose
>>>> document number is greater than or equal
>>>>  to target. Returns the current document number or NO_MORE_DOCS if
>>>> there are no more docs in the set.
>>>> Behaves as if written:
>>>>  int advance(int target) {
>>>>    int doc;
>>>>    while ((doc = nextDoc()) < target) {
>>>>    }
>>>>    return doc;
>>>>  }
>>>>  Some implementations are considerably more efficient than that.
>>>> NOTE: when target < current implementations may opt not to advance
>>>> beyond their current docID().
>>>> NOTE: this method may be called with NO_MORE_DOCS for efficiency by
>>>> some Scorers. If your
>>>>  implementation cannot efficiently determine that it should exhaust, it
>>>> is recommended that you check for
>>>>  that value in each call to this method.
>>>> NOTE: after the iterator has exhausted you should not call this method,
>>>> as it may result in unpredicted
>>>>  behavior.
>>>> --------------------------------------
>>>> Then I modified my algorithm again and found that
>>>> DisjunctionSumScorer.advance(int target) has some strange behavior. most
>>>> the cases, it will return currentDoc if target < currentDoc. but in some
>>>> boundary condition, it will not.
>>>> it's not a bug but let me sad. I thought my algorithm has some bug
>>>> because it's advance method is not exactly the same as original
>>>> DisjunctionSumScorer's.
>>>> ----codes of DisjunctionSumScorer---
>>>>   @Override
>>>>   public int advance(int target) throws IOException {
>>>>     if (scorerDocQueue.size() < minimumNrMatchers) {
>>>>       return currentDoc = NO_MORE_DOCS;
>>>>     }
>>>>     if (target <= currentDoc) {
>>>>       return currentDoc;
>>>>     }
>>>>    ....
>>>> -------------------
>>>> for most case if (target <= currentDoc) it will return currentDoc;
>>>> but if previous advance will make sub scorers exhausted, then if may
>>>> return NO_MORE_DOCS
>>>> an example is:
>>>>    currentDoc=-1
>>>>    minimumNrMatchers=1
>>>>    subScorers:
>>>>       TermScorer: docIds: [1, 2, 6]
>>>>       TermScorer: docIds: [2, 4]
>>>> after first call advance(5)
>>>>     currentDoc=6
>>>>     only first scorer is now in the heap, scorerDocQueue.size()==1
>>>> then call advance(6)
>>>>     because scorerDocQueue.size() < minimumNrMatchers, it just return
>>>> My question is why the advance(int target) method is defined like this?
>>>> for the reason of efficient or any other reasons?
>>> --
>>> Sincerely yours
>>> Mikhail Khludnev
>>> <>
>>>  <>
> --
> Sincerely yours
> Mikhail Khludnev
> <>
>  <>

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