diff --git a/source/net/yacy/cora/storage/ComparableARC.java b/source/net/yacy/cora/storage/ComparableARC.java
index 8d40d0184..31d1aadf5 100644
--- a/source/net/yacy/cora/storage/ComparableARC.java
+++ b/source/net/yacy/cora/storage/ComparableARC.java
@@ -22,6 +22,7 @@
 package net.yacy.cora.storage;
 
 import java.util.Comparator;
+import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.Map;
 import java.util.TreeMap;
@@ -44,25 +45,57 @@ public final class ComparableARC<K, V> extends SimpleARC<K, V> implements Map<K,
             this.limit = cacheSize;
             this.keys = new LinkedList<K>();
         }
-        public V put(K k, V v) {
+        public synchronized V put(K k, V v) {
             V r = super.put(k, v);
-            keys.add(k);
+            if (r == null) keys.add(k);
             if (keys.size() > this.limit) {
                 K w = this.keys.removeFirst();
+                assert w != null;
                 V t = super.remove(w);
-                assert t != null;
+                assert t != null : "keys.size() = " + keys.size() + ", limit = " + this.limit;
             }
             return r;
         }
-        public V remove(Object k) {
+        public void putAll(Map<? extends K, ? extends V> map) {
+            for (Map.Entry<? extends K, ? extends V> entry: map.entrySet()) put(entry.getKey(), entry.getValue());
+        }
+        public synchronized V remove(Object k) {
             V r = super.remove(k);
-            this.keys.remove(k);
+            if (r == null) return null;
+            @SuppressWarnings("unchecked")
+            boolean removed = removeFromKeys((K) k);
+            assert removed;
             return r;
         }
-        public void clear() {
+        public synchronized Map.Entry<K,V> pollFirstEntry() {
+            Map.Entry<K,V> entry = super.pollFirstEntry();
+            boolean removed = removeFromKeys(entry.getKey());
+            assert removed;
+            return entry;
+        }
+        public synchronized Map.Entry<K,V> pollLastEntry() {
+            Map.Entry<K,V> entry = super.pollLastEntry();
+            boolean removed = removeFromKeys(entry.getKey());
+            assert removed;
+            return entry;
+        }
+        public synchronized void clear() {
             super.clear();
             this.keys.clear();
         }
+        private boolean removeFromKeys(K k) {
+            assert k != null;
+            Iterator<K> i = keys.iterator();
+            K x;
+            while (i.hasNext()) {
+                x = i.next();
+                if (super.comparator().compare(k, x) == 0) {
+                    i.remove();
+                    return true;
+                }
+            }
+            return false;
+        }
     }
     
 }
diff --git a/source/net/yacy/cora/storage/ConcurrentARC.java b/source/net/yacy/cora/storage/ConcurrentARC.java
index f8f47f818..bb9b29631 100644
--- a/source/net/yacy/cora/storage/ConcurrentARC.java
+++ b/source/net/yacy/cora/storage/ConcurrentARC.java
@@ -42,6 +42,11 @@ public final class ConcurrentARC<K, V> extends AbstractMap<K, V> implements Map<
     private final int mask;
     private final ARC<K, V> arc[];
     
+    /**
+     * create a concurrent ARC based on a HashARC. The type of the key elements must implement a hashing function
+     * @param cacheSize the number of maximum entries
+     * @param partitions the number of partitions
+     */
     @SuppressWarnings("unchecked")
 	public ConcurrentARC(final int cacheSize, final int partitions) {
     	int m = 1;
@@ -52,6 +57,12 @@ public final class ConcurrentARC<K, V> extends AbstractMap<K, V> implements Map<
     	this.mask = m;
     }
     
+    /**
+     * create a concurrent ARC based on a ComparableARC
+     * @param cacheSize the number of maximum entries
+     * @param partitions the number of partitions
+     * @param comparator a comparator for the key object which may be of type byte[]
+     */
     @SuppressWarnings("unchecked")
     public ConcurrentARC(final int cacheSize, final int partitions, Comparator<? super K> comparator) {
         int m = 1;
diff --git a/source/net/yacy/kelondro/blob/MapHeap.java b/source/net/yacy/kelondro/blob/MapHeap.java
index a2127a83e..fe813e0c5 100644
--- a/source/net/yacy/kelondro/blob/MapHeap.java
+++ b/source/net/yacy/kelondro/blob/MapHeap.java
@@ -55,7 +55,7 @@ import net.yacy.kelondro.util.kelondroException;
 public class MapHeap implements Map<byte[], Map<String, String>> {
 
     private BLOB blob;
-    private ARC<String, Map<String, String>> cache;
+    private ARC<byte[], Map<String, String>> cache;
     private final char fillchar;
 
     
@@ -67,7 +67,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
             final int cachesize,
             char fillchar) throws IOException {
         this.blob = new Heap(heapFile, keylength, ordering, buffermax);
-        this.cache = new ConcurrentARC<String, Map<String, String>>(cachesize, Runtime.getRuntime().availableProcessors());
+        this.cache = new ConcurrentARC<byte[], Map<String, String>>(cachesize, Runtime.getRuntime().availableProcessors(), ordering);
         this.fillchar = fillchar;
     }
    
@@ -147,7 +147,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
         	if (blob != null) blob.insert(key, sb);
     
             // write map to cache
-            if (cache != null) cache.put(new String(key), newMap);
+            if (cache != null) cache.put(key, newMap);
         }
     }
     
@@ -176,7 +176,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
         
         synchronized (this) {
             // remove from cache
-            cache.remove(new String(key));
+            cache.remove(key);
     
             // remove from file
             blob.delete(key);
@@ -208,7 +208,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
         byte[] key = normalizeKey((byte[]) k);
         boolean h;
         synchronized (this) {
-            h = this.cache.containsKey(new String(key)) || this.blob.containsKey(key);
+            h = this.cache.containsKey(key) || this.blob.containsKey(key);
         }
         return h;
     }
@@ -262,8 +262,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
         Map<String, String> map;
         if (storeCache) {
             synchronized (this) {
-                String keys = new String(key);
-                map = cache.get(keys);
+                map = cache.get(key);
                 if (map != null) return map;
     
                 // read object
@@ -276,7 +275,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
                 }
         
                 // write map to cache
-                cache.put(keys, map);
+                cache.put(key, map);
             }
             
             // return value
@@ -284,7 +283,7 @@ public class MapHeap implements Map<byte[], Map<String, String>> {
         } else {
             byte[] b;
             synchronized (this) {
-                map = cache.get(new String(key));
+                map = cache.get(key);
                 if (map != null) return map;
                 b = blob.get(key);
             }