add some log

Signed-off-by: bowenlan-amzn <[email protected]>

server/src/main/java/org/opensearch/search/aggregations/metrics/CardinalityAggregator.java

@@ -166,6 +166,7 @@ private Collector pickCollector(LeafReaderContext ctx) throws IOException {
         if (parent == null && subAggregators.length == 0 && valuesSourceConfig.missing() == null && valuesSourceConfig.script() == null) {
             Terms terms = ctx.reader().terms(valuesSourceConfig.fieldContext().field());
             if (terms != null) {
+                logger.debug("dynamic pruning for shard {} segment {}", context.indexShard().shardId(), ctx.ord);
                 Weight weight = context.searcher().createWeight(context.searcher().rewrite(context.query()), ScoreMode.TOP_DOCS, 1f);
                 Bits liveDocs = ctx.reader().getLiveDocs();
                 BulkScorer scorer = weight.bulkScorer(ctx);
@@ -294,7 +295,11 @@ public void collect(int doc, long owningBucketOrd) throws IOException {
                 } while (queue.size() > 1 && top.doc == curTopDoc);
             }
 
-            logger.debug("after pruning top doc {}", top.doc);
+            if (queue.size() == 0) {
+                logger.debug("queue size is 0");
+            } else {
+                logger.debug("after pruning top doc {}", top.doc);
+            }
             // after pruning, queue top doc will exceed current doc
             // but in the scoring process, we have a contract that every iteration or nextDoc
             // iterator: 0 - 1 - 2 - 3 - ...