Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java	(revision 1724997)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java	(working copy)
@@ -26,6 +26,7 @@
 import com.google.common.base.Function;
 import org.apache.jackrabbit.oak.cache.CacheLIRS;
 import org.apache.jackrabbit.oak.cache.CacheStats;
+import org.apache.jackrabbit.oak.commons.StringUtils;
 
 /**
  * A string cache. It has two components: a fast cache for small strings, based
@@ -83,8 +84,7 @@
             cache.put(key, s, getMemory(s));
         }
         if (FastCache.isSmall(s)) {
-            key.setString(s);
-            fastCache.addString(hash, key);
+            fastCache.addString(hash, key.withValue(s));
         }
         return s;
     }
@@ -98,7 +98,7 @@
     }
 
     private static int getMemory(String s) {
-        return 100 + s.length() * 2;
+        return StringUtils.estimateMemoryUsage(s) + 52;
     }
 
     private static int getEntryHash(long lsb, long msb, int offset) {
@@ -170,7 +170,7 @@
         private final int hash;
         private final long msb, lsb;
         private final int offset;
-        private String string;
+        private final String string;
 
         StringCacheEntry(int hash, long msb, long lsb, int offset, String string) {
             this.hash = hash;
@@ -180,11 +180,11 @@
             this.string = string;
         }
 
-        void setString(String string) {
+        StringCacheEntry withValue(String string) {
             if (string == null) {
                 throw new NullPointerException();
             }
-            this.string = string;
+            return new StringCacheEntry(hash, lsb, msb, offset, string);
         }
 
         boolean matches(long msb, long lsb, int offset) {