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https://issues.apache.org/jira/browse/LUCENE-1821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12745754#action_12745754
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Tim Smith commented on LUCENE-1821:
-----------------------------------
in the case of the getDocIdSet() method, i would say you should pass "0" for
the docBase
This is because in this case, you are asking for DocIdSet in the context of
*reader*
howevever, this method is actually also a bit broken now with per segment
searching
what if *reader* is a MultiReader
This could now incur the "double ram usage" penalty refered to in that
"explain()" ticket i recall seeing last week
If *query* has any ValueSource based queries, it'll result in getting the
ValueSource in the context of the MultiReader (if i'm not mistaken)
So, this method in particular should probably be rewritten to return a
DocIdSetIterator that will step through each segment in "reader" in turn
> Weight.scorer() not passed doc offset for "sub reader"
> ------------------------------------------------------
>
> Key: LUCENE-1821
> URL: https://issues.apache.org/jira/browse/LUCENE-1821
> Project: Lucene - Java
> Issue Type: Bug
> Components: Search
> Affects Versions: 2.9
> Reporter: Tim Smith
> Fix For: 2.9
>
> Attachments: LUCENE-1821.patch
>
>
> Now that searching is done on a per segment basis, there is no way for a
> Scorer to know the "actual" doc id for the document's it matches (only the
> relative doc offset into the segment)
> If using caches in your scorer that are based on the "entire" index (all
> segments), there is now no way to index into them properly from inside a
> Scorer because the scorer is not passed the needed offset to calculate the
> "real" docid
> suggest having Weight.scorer() method also take a integer for the doc offset
> Abstract Weight class should have a constructor that takes this offset as
> well as a method to get the offset
> All Weights that have "sub" weights must pass this offset down to created
> "sub" weights
> Details on workaround:
> In order to work around this, you must do the following:
> * Subclass IndexSearcher
> * Add "int getIndexReaderBase(IndexReader)" method to your subclass
> * during Weight creation, the Weight must hold onto a reference to the passed
> in Searcher (casted to your sub class)
> * during Scorer creation, the Scorer must be passed the result of
> YourSearcher.getIndexReaderBase(reader)
> * Scorer can now rebase any collected docids using this offset
> Example implementation of getIndexReaderBase():
> {code}
> // NOTE: more efficient implementation can be done if you cache the result if
> gatherSubReaders in your constructor
> public int getIndexReaderBase(IndexReader reader) {
> if (reader == getReader()) {
> return 0;
> } else {
> List readers = new ArrayList();
> gatherSubReaders(readers);
> Iterator iter = readers.iterator();
> int maxDoc = 0;
> while (iter.hasNext()) {
> IndexReader r = (IndexReader)iter.next();
> if (r == reader) {
> return maxDoc;
> }
> maxDoc += r.maxDoc();
> }
> }
> return -1; // reader not in searcher
> }
> {code}
> Notes:
> * This workaround makes it so you cannot serialize your custom Weight
> implementation
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