Fix HNSW InfoStream duplicate times and add per-chunk completion logging (#15967)

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

Author: iprithv

lucene/CHANGES.txt

@@ -148,6 +148,9 @@ Optimizations
 
 Bug Fixes
 ---------------------
+* GITHUB#15967: Fix InfoStream progress lines from concurrent HNSW merging reporting duplicate
+  times, and add per-chunk completion logging to aid concurrency debugging. (Prithvi S)
+
 * GITHUB#14049: Randomize KNN codec params in RandomCodec. Fixes scalar quantization div-by-zero
   when all values are identical. (Mike Sokolov)
 

lucene/core/src/java/org/apache/lucene/util/hnsw/HnswGraphBuilder.java

@@ -205,15 +205,27 @@ protected void addVectors(int minOrd, int maxOrd) throws IOException {
       throw new IllegalStateException("This HnswGraphBuilder is frozen and cannot be updated");
     }
     long start = System.nanoTime(), t = start;
-    if (infoStream.isEnabled(HNSW_COMPONENT)) {
-      infoStream.message(HNSW_COMPONENT, "addVectors [" + minOrd + " " + maxOrd + ")");
-    }
+    int numVectors = maxOrd - minOrd;
     for (int node = minOrd; node < maxOrd; node++) {
       addGraphNode(node);
-      if ((node % 10000 == 0) && infoStream.isEnabled(HNSW_COMPONENT)) {
+      // Skip in-loop progress for ranges <= 10000 where it would fire at most once
+      // with identical incremental/total times (#15967).
+      if (numVectors > 10000 && (node % 10000 == 0) && infoStream.isEnabled(HNSW_COMPONENT)) {
         t = printGraphBuildStatus(node, start, t);
       }
     }
+    if (infoStream.isEnabled(HNSW_COMPONENT)) {
+      long elapsed = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
+      infoStream.message(
+          HNSW_COMPONENT,
+          String.format(
+              Locale.ROOT,
+              "addVectors [%d %d): %d vectors in %d ms",
+              minOrd,
+              maxOrd,
+              numVectors,
+              elapsed));
+    }
   }
 
   private void addVectors(int maxOrd) throws IOException {