Hi, IndexSearcher.search(Query, Collector) will iterate through all segments of the index, call getLeafCollector, and use the returned LeafCollector to collect result documents from that segment [1].
As LeafCollector's javadoc describes [2], there are cases when you want to take into account precisely which segment you are processing, but sometimes it doesn't matter. Depending on that, you can either return the same LeafCollector instance from getLeafCollector all the time, or create new ones each time it is called, using LeafReaderContext to extract segment-specific values like docBase, or the LeafReader for that segment. These can then be passed down to the custom LeafCollector, stored in fields, and used when collect(int) callbacks occur. The example code in javadoc uses docBase from LeafReaderContext to map segment-relative docIDs to absolute ones. [1] https://github.com/apache/lucene-solr/blob/trunk/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java#L609 [2] https://github.com/apache/lucene-solr/blob/trunk/lucene/core/src/java/org/apache/lucene/search/LeafCollector.java -- András On Sun, Jun 28, 2015 at 5:03 AM, Selva Kumar <selva.kumar.at.w...@gmail.com> wrote: > With wrapping collector scenarios, wrapping LeafCollector needs access to > wrapped LeafCollector. > > If wrapping LeafCollector has access to LeafReaderContext, it seems one can > use getLeafCollector "getter" anytime to get the wrapped leaf collector. > > if collect(int doc) method retrieves LeafCollector on every call, this does > not work since getLeafCollector behaves more like a prototype factory. > > Question: > > If I am writing a new Collector, is it fair to assume getLeafCollector will > be called only once per segment. >
