LUCENE-9674: Use binary search in VectorValues.advance()

Lucene90VectorReader now implements advance() with binary search in place of prior linear scan
Co-authored-by: Anand Kotriwal <[email protected]>

Author: codaitya

lucene/CHANGES.txt

@@ -180,6 +180,9 @@ Improvements
 * LUCENE-8982: Make NativeUnixDirectory pure java with FileChannel direct IO flag,
   and rename to DirectIODirectory (Zach Chen, Uwe Schindler, Mike McCandless, Dawid Weiss).
 
+* LUCENE-9674: Implement faster advance on VectorValues using binary search.
+  (Anand Kotriwal, Mike Sokolov)
+
 Bug fixes
 
 * LUCENE-8663: NRTCachingDirectory.slowFileExists may open a file while 

lucene/core/src/java/org/apache/lucene/codecs/lucene90/Lucene90VectorReader.java

@@ -22,6 +22,7 @@
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.FloatBuffer;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Random;
@@ -386,9 +387,19 @@ public int nextDoc() {
     }
 
     @Override
-    public int advance(int target) throws IOException {
-      // We could do better by log-binary search in ordToDoc, but this is never used
-      return slowAdvance(target);
+    public int advance(int target) {
+      assert docID() < target;
+      ord = Arrays.binarySearch(fieldEntry.ordToDoc, ord + 1, fieldEntry.ordToDoc.length, target);
+      if (ord < 0) {
+        ord = -(ord + 1);
+      }
+      assert ord >= 0 && ord <= fieldEntry.ordToDoc.length;
+      if (ord == fieldEntry.ordToDoc.length) {
+        doc = NO_MORE_DOCS;
+      } else {
+        doc = fieldEntry.ordToDoc[ord];
+      }
+      return doc;
     }
 
     @Override

lucene/core/src/test/org/apache/lucene/index/TestVectorValues.java

@@ -815,4 +815,50 @@ public void testSearchStrategyIdentifiers() {
     assertEquals(2, VectorValues.SearchStrategy.DOT_PRODUCT_HNSW.ordinal());
     assertEquals(3, VectorValues.SearchStrategy.values().length);
   }
+
+  public void testAdvance() throws Exception {
+    try (Directory dir = newDirectory()) {
+      try (IndexWriter w = new IndexWriter(dir, createIndexWriterConfig())) {
+        int numdocs = atLeast(1500);
+        String fieldName = "field";
+        for (int i = 0; i < numdocs; i++) {
+          Document doc = new Document();
+          // randomly add a vector field
+          if (random().nextInt(4) == 3) {
+            doc.add(new VectorField(fieldName, new float[4], SearchStrategy.NONE));
+          }
+          w.addDocument(doc);
+        }
+        w.forceMerge(1);
+        try (IndexReader reader = w.getReader()) {
+          LeafReader r = getOnlyLeafReader(reader);
+          VectorValues vectorValues = r.getVectorValues(fieldName);
+          int[] vectorDocs = new int[vectorValues.size() + 1];
+          int cur = -1;
+          while (++cur < vectorValues.size() + 1) {
+            vectorDocs[cur] = vectorValues.nextDoc();
+            if (cur != 0) {
+              assertTrue(vectorDocs[cur] > vectorDocs[cur - 1]);
+            }
+          }
+          vectorValues = r.getVectorValues(fieldName);
+          cur = -1;
+          for (int i = 0; i < numdocs; i++) {
+            // randomly advance to i
+            if (random().nextInt(4) == 3) {
+              while (vectorDocs[++cur] < i)
+                ;
+              assertEquals(vectorDocs[cur], vectorValues.advance(i));
+              assertEquals(vectorDocs[cur], vectorValues.docID());
+              if (vectorValues.docID() == NO_MORE_DOCS) {
+                break;
+              }
+              // make i equal to docid so that it is greater than docId in the next loop iteration
+              i = vectorValues.docID();
+            }
+          }
+        }
+      }
+    }
+  }
 }