LUCENE-7099: speed up embarrasingly slow sandbox/ distance sort

lucene/sandbox/src/java/org/apache/lucene/document/LatLonPointDistanceComparator.java

@@ -27,8 +27,16 @@ import org.apache.lucene.search.FieldComparator;
 import org.apache.lucene.search.LeafFieldComparator;
 import org.apache.lucene.search.Scorer;
 import org.apache.lucene.spatial.util.GeoDistanceUtils;
+import org.apache.lucene.spatial.util.GeoRect;
+import org.apache.lucene.spatial.util.GeoUtils;
 
-/** Compares docs by distance from an origin */
+/**
+ * Compares documents by distance from an origin point
+ * <p>
+ * When the least competitive item on the priority queue changes (setBottom), we recompute
+ * a bounding box representing competitive distance to the top-N. Then in compareBottom, we can
+ * quickly reject hits based on bounding box alone without computing distance for every element.
+ */
 class LatLonPointDistanceComparator extends FieldComparator<Double> implements LeafFieldComparator {
   final String field;
   final double latitude;
@@ -40,6 +48,24 @@ class LatLonPointDistanceComparator extends FieldComparator<Double> implements L
   double topValue;
   SortedNumericDocValues currentDocs;
   
+  // current bounding box(es) for the bottom distance on the PQ.
+  // these are pre-encoded with LatLonPoint's encoding and 
+  // used to exclude uncompetitive hits faster.
+  int minLon;
+  int maxLon;
+  int minLat;
+  int maxLat;
+
+  // crossesDateLine is true, then we have a second box to check
+  boolean crossesDateLine;
+  int minLon2;
+  int maxLon2;
+  int minLat2;
+  int maxLat2;
+
+  // the number of times setBottom has been called (adversary protection)
+  int setBottomCounter = 0;
+
   public LatLonPointDistanceComparator(String field, double latitude, double longitude, int numHits, double missingValue) {
     this.field = field;
     this.latitude = latitude;
@@ -59,6 +85,52 @@ class LatLonPointDistanceComparator extends FieldComparator<Double> implements L
   @Override
   public void setBottom(int slot) {
     bottom = values[slot];
+    // make bounding box(es) to exclude non-competitive hits, but start
+    // sampling if we get called way too much: don't make gobs of bounding
+    // boxes if comparator hits a worst case order (e.g. backwards distance order)
+    if (setBottomCounter < 1024 || (setBottomCounter & 0x3F) == 0x3F) {
+      GeoRect box = GeoUtils.circleToBBox(longitude, latitude, bottom);
+      // pre-encode our box to our integer encoding, so we don't have to decode 
+      // to double values for uncompetitive hits. This has some cost!
+      int minLatEncoded = LatLonPoint.encodeLatitude(box.minLat);
+      int maxLatEncoded = LatLonPoint.encodeLatitude(box.maxLat);
+      int minLonEncoded = LatLonPoint.encodeLongitude(box.minLon);
+      int maxLonEncoded = LatLonPoint.encodeLongitude(box.maxLon);
+      // be sure to not introduce quantization error in our optimization, just 
+      // round up our encoded box safely in all directions.
+      if (minLatEncoded != Integer.MIN_VALUE) {
+        minLatEncoded--;
+      }
+      if (minLonEncoded != Integer.MIN_VALUE) {
+        minLonEncoded--;
+      }
+      if (maxLatEncoded != Integer.MAX_VALUE) {
+        maxLatEncoded++;
+      }
+      if (maxLonEncoded != Integer.MAX_VALUE) {
+        maxLonEncoded++;
+      }
+      crossesDateLine = box.crossesDateline();
+      // crosses dateline: split
+      if (crossesDateLine) {
+        // box1
+        minLon = Integer.MIN_VALUE;
+        maxLon = maxLonEncoded;
+        minLat = minLatEncoded;
+        maxLat = maxLatEncoded;
+        // box2
+        minLon2 = minLonEncoded;
+        maxLon2 = Integer.MAX_VALUE;
+        minLat2 = minLatEncoded;
+        maxLat2 = maxLatEncoded;
+      } else {
+        minLon = minLonEncoded;
+        maxLon = maxLonEncoded;
+        minLat = minLatEncoded;
+        maxLat = maxLatEncoded;
+      }
+    }
+    setBottomCounter++;
   }
   
   @Override
@@ -68,7 +140,28 @@ class LatLonPointDistanceComparator extends FieldComparator<Double> implements L
   
   @Override
   public int compareBottom(int doc) throws IOException {
-    return Double.compare(bottom, distance(doc));
+    currentDocs.setDocument(doc);
+
+    int numValues = currentDocs.count();
+    if (numValues == 0) {
+      return Double.compare(bottom, missingValue);
+    }
+
+    double minValue = Double.POSITIVE_INFINITY;
+    for (int i = 0; i < numValues; i++) {
+      long encoded = currentDocs.valueAt(i);
+      int latitudeBits = (int)(encoded >> 32);
+      int longitudeBits = (int)(encoded & 0xFFFFFFFF);
+      boolean outsideBox = ((latitudeBits < minLat || longitudeBits < minLon || latitudeBits > maxLat || longitudeBits > maxLon) &&
+            (crossesDateLine == false || latitudeBits < minLat2 || longitudeBits < minLon2 || latitudeBits > maxLat2 || longitudeBits > maxLon2));
+      // only compute actual distance if its inside "competitive bounding box"
+      if (outsideBox == false) {
+        double docLatitude = LatLonPoint.decodeLatitude(latitudeBits);
+        double docLongitude = LatLonPoint.decodeLongitude(longitudeBits);
+        minValue = Math.min(minValue, GeoDistanceUtils.haversin(latitude, longitude, docLatitude, docLongitude));
+      }
+    }
+    return Double.compare(bottom, minValue);
   }
   
   @Override