LUCENE-10129: Add RamUsageEstimator.shallowSizeOf() for primitive arrays (#367)

Co-authored-by: Stefan Vodita <voditas@amazon.com>

lucene/CHANGES.txt

@@ -163,6 +163,10 @@ API Changes
 
 Improvements
 
+* LUCENE-10129: RamUsageEstimator overloads the shallowSizeOf method for primitive arrays
+  to avoid falling back on shallowSizeOf(Object), which could lead to performance traps.
+  (Robert Muir, Uwe Schindler, Stefan Vodita)
+
 * LUCENE-10139: ExternalRefSorter returns a covariant with a subtype of BytesRefIterator
   that is Closeable. (Dawid Weiss).
 

lucene/core/src/java/org/apache/lucene/util/RamUsageEstimator.java

@@ -486,6 +486,46 @@ public final class RamUsageEstimator {
     return alignObjectSize(size);
   }
 
+  /** Returns the size in bytes of the byte[] object. */
+  public static long shallowSizeOf(byte[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the boolean[] object. */
+  public static long shallowSizeOf(boolean[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the char[] object. */
+  public static long shallowSizeOf(char[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the short[] object. */
+  public static long shallowSizeOf(short[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the int[] object. */
+  public static long shallowSizeOf(int[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the float[] object. */
+  public static long shallowSizeOf(float[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the long[] object. */
+  public static long shallowSizeOf(long[] arr) {
+    return sizeOf(arr);
+  }
+
+  /** Returns the size in bytes of the double[] object. */
+  public static long shallowSizeOf(double[] arr) {
+    return sizeOf(arr);
+  }
+
   /** Returns the shallow size in bytes of the Object[] object. */
   // Use this method instead of #shallowSizeOf(Object) to avoid costly reflection
   public static long shallowSizeOf(Object[] arr) {

lucene/core/src/test/org/apache/lucene/util/TestRamUsageEstimator.java

@@ -65,41 +65,49 @@ public class TestRamUsageEstimator extends LuceneTestCase {
     {
       byte[] array = new byte[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       boolean[] array = new boolean[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       char[] array = new char[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       short[] array = new short[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       int[] array = new int[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       float[] array = new float[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       long[] array = new long[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
 
     {
       double[] array = new double[rnd.nextInt(1024)];
       assertEquals(sizeOf(array), sizeOf((Object) array));
+      assertEquals(shallowSizeOf(array), sizeOf((Object) array));
     }
   }