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https://issues.apache.org/jira/browse/LUCENE-1821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12746635#action_12746635
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Michael McCandless commented on LUCENE-1821:
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bq. one used a cached DocIdSet created over the top level MultiReader (should
be able to have a DocIdSet per Segment reader here, but this will take some
more thinking (source of the matching docids is from a separate index), will
also need to know which sub docidset to use based on which IndexReader is
passed to scorer() - shouldn't be any big deal)
I think, similarly, you could continue to create the top-level
DocIdSet, but then make a new DocIdSet that presents one segment's
"slice" out of this top-level DocIdSet. Then, pre-build the mapping
of IndexReader -> docBase like above, then when scorer() is called in
your custom query, just return the "virtual" per-segment DocIdSet.
Would this work?
> 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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