slow-J commented on code in PR #16271:
URL: https://github.com/apache/lucene/pull/16271#discussion_r3497891276
##########
lucene/core/src/java/org/apache/lucene/search/AbstractKnnVectorQuery.java:
##########
@@ -149,9 +149,64 @@ public Query rewrite(IndexSearcher indexSearcher) throws
IOException {
topK = runSearchTasks(tasks, taskExecutor, perLeafResults,
leafReaderContexts);
}
if (topK.scoreDocs.length == 0) {
- return MatchNoDocsQuery.INSTANCE;
+ return new MatchNoDocsQuery("No documents matched the nearest-neighbor
search");
}
- return DocAndScoreQuery.createDocAndScoreQuery(reader, topK, reentryCount);
+ return DocAndScoreQuery.createDocAndScoreQuery(
+ reader, topK, reentryCount, noMatchExplainer(topK, filterWeight));
+ }
+
+ /** Builds the explainer for documents this query did not collect, capturing
minTopKScore. */
+ private DocAndScoreQuery.NoMatchExplainer noMatchExplainer(TopDocs topK,
Weight filterWeight) {
+ // topK is score-descending, so the lowest collected score is the last
entry.
+ final float minTopKScore = topK.scoreDocs[topK.scoreDocs.length - 1].score;
+ return (context, doc, topN) ->
+ explainNotCollected(context, doc, topN, filterWeight, minTopKScore);
+ }
+
+ /** Explains why a doc was not collected, by recomputing its score. null
when no vectors. */
+ private Explanation explainNotCollected(
+ LeafReaderContext context, int doc, int topN, Weight filterWeight, float
minTopKScore)
+ throws IOException {
+ String prefix = "Not in top " + topN + " doc(s): ";
+ FieldInfo fi = context.reader().getFieldInfos().fieldInfo(field);
+ if (fi == null || fi.getVectorDimension() == 0) {
+ return null;
Review Comment:
It would fall back to the generic `"Not in top " + docs.length + " doc(s)`,
in DocAndScoreQuery's createWeight#explain
https://github.com/slow-J/lucene/blob/KNNexplain/lucene/core/src/java/org/apache/lucene/search/DocAndScoreQuery.java#L164
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