add entries iterator to ValueHashMap

speeds up this query by about 30%

h2/src/main/org/h2/command/dml/Select.java

@@ -28,6 +28,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Map;
 
 /**
  * This class represents a simple SELECT statement.
@@ -420,10 +421,9 @@ public class Select extends Query {
                 groupByData.put(defaultGroup,
                         new Object[Math.max(exprToIndexInGroupByData.size(), expressions.size())]);
             }
-            ArrayList<Value> keys = groupByData.keys();
-            for (Value v : keys) {
-                currentGroupsKey = (ValueArray) v;
-                currentGroupByExprData = groupByData.get(currentGroupsKey);
+            for (Map.Entry<Value, Object[]> entry : groupByData.entries()) {
+                currentGroupsKey = (ValueArray) entry.getKey();
+                currentGroupByExprData = entry.getValue();
                 Value[] keyValues = currentGroupsKey.getList();
                 Value[] row = new Value[columnCount];
                 for (int j = 0; groupIndex != null && j < groupIndex.length; j++) {

h2/src/main/org/h2/util/ValueHashMap.java

@@ -6,7 +6,10 @@
 package org.h2.util;
 
 import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.Map;
 import org.h2.message.DbException;
+import org.h2.mvstore.DataUtils;
 import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
@@ -189,6 +192,39 @@ public class ValueHashMap<V> extends HashBase {
         return list;
     }
     
+    public Iterable<Map.Entry<Value, V>> entries() {
+        return new EntryIterable();
+    }
+    
+    private final class EntryIterable implements Iterable<Map.Entry<Value, V>> {
+        @Override
+        public Iterator<Map.Entry<Value, V>> iterator() {
+            return new EntryIterator();
+        }
+    }
+
+    private final class EntryIterator implements Iterator<Map.Entry<Value, V>> {
+        int keysIndex = -1;
+
+        @Override
+        public boolean hasNext() {
+            if (keysIndex >= keys.length)
+                return false;
+            do {
+                keysIndex++;
+                if (keysIndex >= keys.length)
+                    return false;
+                if (keys[keysIndex] != null && keys[keysIndex] != ValueNull.DELETED)
+                    return true;
+            } while (true);
+        }
+
+        @Override
+        public Map.Entry<Value, V> next() {
+            return new DataUtils.MapEntry<Value, V>(keys[keysIndex], values[keysIndex]);
+        }
+    }
+
     /**
      * Get the list of values.
      *