GH-52: Make RangeEqualsVisitor of RunEndEncodedVector more efficient (#761)

## What's Changed

Avoid doing a binary search on every step to make the RangeEqualsVisitor
of RunEndEncodedVector more efficient.

Closes #52 .

Author: ViggoC

vector/src/main/java/org/apache/arrow/vector/compare/RangeEqualsVisitor.java

@@ -43,6 +43,7 @@
 import org.apache.arrow.vector.complex.ListViewVector;
 import org.apache.arrow.vector.complex.NonNullableStructVector;
 import org.apache.arrow.vector.complex.RunEndEncodedVector;
+import org.apache.arrow.vector.complex.RunEndEncodedVector.RangeIterator;
 import org.apache.arrow.vector.complex.StructVector;
 import org.apache.arrow.vector.complex.UnionVector;
 
@@ -270,42 +271,35 @@ protected boolean compareRunEndEncodedVectors(Range range) {
     RunEndEncodedVector leftVector = (RunEndEncodedVector) left;
     RunEndEncodedVector rightVector = (RunEndEncodedVector) right;
 
-    final int leftRangeEnd = range.getLeftStart() + range.getLength();
-    final int rightRangeEnd = range.getRightStart() + range.getLength();
+    final RunEndEncodedVector.RangeIterator leftIterator =
+        new RunEndEncodedVector.RangeIterator(leftVector, range.getLeftStart(), range.getLength());
+    final RunEndEncodedVector.RangeIterator rightIterator =
+        new RunEndEncodedVector.RangeIterator(
+            rightVector, range.getRightStart(), range.getLength());
 
     FieldVector leftValuesVector = leftVector.getValuesVector();
     FieldVector rightValuesVector = rightVector.getValuesVector();
 
     RangeEqualsVisitor innerVisitor = createInnerVisitor(leftValuesVector, rightValuesVector, null);
 
-    int leftLogicalIndex = range.getLeftStart();
-    int rightLogicalIndex = range.getRightStart();
+    while (nextRun(leftIterator, rightIterator)) {
+      int leftPhysicalIndex = leftIterator.getRunIndex();
+      int rightPhysicalIndex = rightIterator.getRunIndex();
 
-    while (leftLogicalIndex < leftRangeEnd) {
-      // TODO: implement it more efficient
-      // https://github.com/apache/arrow/issues/44157
-      int leftPhysicalIndex = leftVector.getPhysicalIndex(leftLogicalIndex);
-      int rightPhysicalIndex = rightVector.getPhysicalIndex(rightLogicalIndex);
-      if (leftValuesVector.accept(
-          innerVisitor, new Range(leftPhysicalIndex, rightPhysicalIndex, 1))) {
-        int leftRunEnd = leftVector.getRunEnd(leftLogicalIndex);
-        int rightRunEnd = rightVector.getRunEnd(rightLogicalIndex);
-
-        int leftRunLength = Math.min(leftRunEnd, leftRangeEnd) - leftLogicalIndex;
-        int rightRunLength = Math.min(rightRunEnd, rightRangeEnd) - rightLogicalIndex;
-
-        if (leftRunLength != rightRunLength) {
-          return false;
-        } else {
-          leftLogicalIndex = leftRunEnd;
-          rightLogicalIndex = rightRunEnd;
-        }
-      } else {
+      if (leftIterator.getRunLength() != rightIterator.getRunLength()
+          || !leftValuesVector.accept(
+              innerVisitor, new Range(leftPhysicalIndex, rightPhysicalIndex, 1))) {
         return false;
       }
     }
 
-    return true;
+    return leftIterator.isEnd() && rightIterator.isEnd();
+  }
+
+  private static boolean nextRun(RangeIterator leftIterator, RangeIterator rightIterator) {
+    boolean left = leftIterator.nextRun();
+    boolean right = rightIterator.nextRun();
+    return left && right;
   }
 
   protected RangeEqualsVisitor createInnerVisitor(

vector/src/main/java/org/apache/arrow/vector/complex/RunEndEncodedVector.java

@@ -28,6 +28,7 @@
 import org.apache.arrow.memory.OutOfMemoryException;
 import org.apache.arrow.memory.util.ByteFunctionHelpers;
 import org.apache.arrow.memory.util.hash.ArrowBufHasher;
+import org.apache.arrow.util.Preconditions;
 import org.apache.arrow.vector.BaseIntVector;
 import org.apache.arrow.vector.BaseValueVector;
 import org.apache.arrow.vector.BigIntVector;
@@ -820,4 +821,101 @@ static int getPhysicalIndex(FieldVector runEndVector, int logicalIndex) {
 
     return result;
   }
+
+  public static class RangeIterator {
+
+    private final RunEndEncodedVector runEndEncodedVector;
+    private final int rangeEnd;
+    private int runIndex;
+    private int runEnd;
+    private int logicalPos;
+
+    /**
+     * Constructs a new RangeIterator for iterating over a range of values in a RunEndEncodedVector.
+     *
+     * @param runEndEncodedVector The vector to iterate over
+     * @param startIndex The logical start index of the range (inclusive)
+     * @param length The number of values to include in the range
+     * @throws IllegalArgumentException if startIndex is negative or (startIndex + length) exceeds
+     *     vector bounds
+     */
+    public RangeIterator(RunEndEncodedVector runEndEncodedVector, int startIndex, int length) {
+      int rangeEnd = startIndex + length;
+      Preconditions.checkArgument(
+          startIndex >= 0, "startIndex %s must be non negative.", startIndex);
+      Preconditions.checkArgument(
+          rangeEnd <= runEndEncodedVector.getValueCount(),
+          "(startIndex + length) %s out of range[0, %s].",
+          rangeEnd,
+          runEndEncodedVector.getValueCount());
+
+      this.rangeEnd = rangeEnd;
+      this.runEndEncodedVector = runEndEncodedVector;
+      this.runIndex = runEndEncodedVector.getPhysicalIndex(startIndex) - 1;
+      this.runEnd = startIndex;
+      this.logicalPos = -1;
+    }
+
+    /**
+     * Advances to the next run in the range.
+     *
+     * @return true if there is another run available, false if iteration has completed
+     */
+    public boolean nextRun() {
+      logicalPos = runEnd;
+      if (logicalPos >= rangeEnd) {
+        return false;
+      }
+      updateRun();
+      return true;
+    }
+
+    private void updateRun() {
+      runIndex++;
+      runEnd = (int) ((BaseIntVector) runEndEncodedVector.runEndsVector).getValueAsLong(runIndex);
+    }
+
+    /**
+     * Advances to the next value in the range.
+     *
+     * @return true if there is another value available, false if iteration has completed
+     */
+    public boolean nextValue() {
+      logicalPos++;
+      if (logicalPos >= rangeEnd) {
+        return false;
+      }
+      if (logicalPos == runEnd) {
+        updateRun();
+      }
+      return true;
+    }
+
+    /**
+     * Gets the current run index (physical position in the run-ends vector).
+     *
+     * @return the current run index
+     */
+    public int getRunIndex() {
+      return runIndex;
+    }
+
+    /**
+     * Gets the length of the current run within the iterator's range.
+     *
+     * @return the number of remaining values in current run within the iterator's range
+     */
+    public int getRunLength() {
+      return Math.min(runEnd, rangeEnd) - logicalPos;
+    }
+
+    /**
+     * Checks if iteration has completed.
+     *
+     * @return true if all values in the range have been processed, false otherwise
+     */
+    public boolean isEnd() {
+      return logicalPos >= rangeEnd;
+    }
+  }
 }

vector/src/test/java/org/apache/arrow/vector/TestRunEndEncodedVector.java

@@ -148,12 +148,18 @@ public void testRangeCompare() {
     assertTrue(
         constantVector.accept(
             new RangeEqualsVisitor(constantVector, constantVector), new Range(1, 2, 13)));
-    assertFalse(
-        constantVector.accept(
-            new RangeEqualsVisitor(constantVector, constantVector), new Range(1, 10, 10)));
-    assertFalse(
-        constantVector.accept(
-            new RangeEqualsVisitor(constantVector, constantVector), new Range(10, 1, 10)));
+
+    // throws exception if the range end is out the bound of the vector
+    assertThrows(
+        IllegalArgumentException.class,
+        () ->
+            constantVector.accept(
+                new RangeEqualsVisitor(constantVector, constantVector), new Range(1, 10, 10)));
+    assertThrows(
+        IllegalArgumentException.class,
+        () ->
+            constantVector.accept(
+                new RangeEqualsVisitor(constantVector, constantVector), new Range(10, 1, 10)));
 
     // Create REE vector representing: [1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5].
     RunEndEncodedVector reeVector =

vector/src/test/java/org/apache/arrow/vector/compare/TestRangeEqualsVisitor.java

@@ -22,6 +22,7 @@
 
 import java.nio.charset.Charset;
 import java.util.Arrays;
+import java.util.List;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.arrow.vector.BigIntVector;
@@ -39,6 +40,7 @@
 import org.apache.arrow.vector.complex.LargeListViewVector;
 import org.apache.arrow.vector.complex.ListVector;
 import org.apache.arrow.vector.complex.ListViewVector;
+import org.apache.arrow.vector.complex.RunEndEncodedVector;
 import org.apache.arrow.vector.complex.StructVector;
 import org.apache.arrow.vector.complex.UnionVector;
 import org.apache.arrow.vector.complex.impl.NullableStructWriter;
@@ -53,7 +55,9 @@
 import org.apache.arrow.vector.holders.NullableUInt4Holder;
 import org.apache.arrow.vector.types.FloatingPointPrecision;
 import org.apache.arrow.vector.types.Types;
+import org.apache.arrow.vector.types.Types.MinorType;
 import org.apache.arrow.vector.types.pojo.ArrowType;
+import org.apache.arrow.vector.types.pojo.ArrowType.RunEndEncoded;
 import org.apache.arrow.vector.types.pojo.Field;
 import org.apache.arrow.vector.types.pojo.FieldType;
 import org.junit.jupiter.api.AfterEach;
@@ -1003,6 +1007,54 @@ public void testLargeListViewVectorApproxEquals() {
     }
   }
 
+  @Test
+  public void testRunEndEncodedFloat8ApproxEquals() {
+    try (final Float8Vector vector1 = new Float8Vector("float", allocator);
+        final Float8Vector vector2 = new Float8Vector("float", allocator);
+        final Float8Vector vector3 = new Float8Vector("float", allocator);
+        final IntVector reeVector = new IntVector("ree", allocator)) {
+
+      final float epsilon = 1.0E-6f;
+      setVector(vector1, 1.1, 2.2);
+      setVector(vector2, 1.1 + epsilon / 2, 2.2 + epsilon / 2);
+      setVector(vector3, 1.1 + epsilon * 2, 2.2 + epsilon * 2);
+      setVector(reeVector, 1, 3);
+
+      ArrowType type = MinorType.FLOAT8.getType();
+      final FieldType valueType = FieldType.notNullable(type);
+      final FieldType runEndType = FieldType.notNullable(MinorType.INT.getType());
+
+      final Field valueField = new Field("value", valueType, null);
+      final Field runEndField = new Field("ree", runEndType, null);
+
+      Field field =
+          new Field(
+              "ree_float",
+              FieldType.notNullable(RunEndEncoded.INSTANCE),
+              List.of(runEndField, valueField));
+
+      try (final RunEndEncodedVector encodedVector1 =
+              new RunEndEncodedVector(field, allocator, reeVector, vector1, null);
+          final RunEndEncodedVector encodedVector2 =
+              new RunEndEncodedVector(field, allocator, reeVector, vector2, null);
+          final RunEndEncodedVector encodedVector3 =
+              new RunEndEncodedVector(field, allocator, reeVector, vector3, null)) {
+
+        encodedVector1.setValueCount(3);
+        encodedVector2.setValueCount(3);
+        encodedVector3.setValueCount(3);
+
+        Range range = new Range(0, 0, encodedVector1.getValueCount());
+        assertTrue(
+            new ApproxEqualsVisitor(encodedVector1, encodedVector2, epsilon, epsilon)
+                .rangeEquals(range));
+        assertFalse(
+            new ApproxEqualsVisitor(encodedVector1, encodedVector3, epsilon, epsilon)
+                .rangeEquals(range));
+      }
+    }
+  }
+
   private void writeStructVector(NullableStructWriter writer, int value1, long value2) {
     writer.start();
     writer.integer("f0").writeInt(value1);