Index: src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java
===================================================================
--- src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java	(revision 1725882)
+++ src/main/java/org/apache/jackrabbit/oak/plugins/segment/StringCache.java	(working copy)
@@ -19,14 +19,17 @@
 
 package org.apache.jackrabbit.oak.plugins.segment;
 
+import static org.apache.jackrabbit.oak.commons.StringUtils.estimateMemoryUsage;
+
 import java.util.Arrays;
 
 import javax.annotation.Nonnull;
 
-import com.google.common.base.Function;
 import org.apache.jackrabbit.oak.cache.CacheLIRS;
 import org.apache.jackrabbit.oak.cache.CacheStats;
 
+import com.google.common.base.Function;
+
 /**
  * A string cache. It has two components: a fast cache for small strings, based
  * on an array, and a slow cache that uses a LIRS cache.
@@ -41,7 +44,7 @@
     /**
      * The slower (LIRS) cache.
      */
-    private final CacheLIRS<StringCacheEntry, String> cache;
+    private final CacheLIRS<StringCacheKey, String> cache;
 
     /**
      * Create a new string cache.
@@ -49,7 +52,7 @@
      * @param maxSize the maximum memory in bytes.
      */
     StringCache(long maxSize) {
-        cache = CacheLIRS.<StringCacheEntry, String>newBuilder()
+        cache = CacheLIRS.<StringCacheKey, String>newBuilder()
                 .module("StringCache")
                 .maximumWeight(maxSize)
                 .averageWeight(100)
@@ -76,15 +79,15 @@
         if (s != null) {
             return s;
         }
-        StringCacheEntry key = new StringCacheEntry(hash, msb, lsb, offset, null);
+        StringCacheKey key = new StringCacheKey(hash, msb, lsb, offset);
         s = cache.getIfPresent(key);
         if (s == null) {
             s = loader.apply(offset);
             cache.put(key, s, getMemory(s));
         }
         if (FastCache.isSmall(s)) {
-            key.setString(s);
-            fastCache.addString(hash, key);
+            fastCache.addString(hash, new FastCacheEntry(hash, msb, lsb,
+                    offset, s));
         }
         return s;
     }
@@ -98,7 +101,7 @@
     }
 
     private static int getMemory(String s) {
-        return 100 + s.length() * 2;
+        return estimateMemoryUsage(s) + 52;
     }
 
     private static int getEntryHash(long lsb, long msb, int offset) {
@@ -125,7 +128,7 @@
         /**
          * The cache array.
          */
-        private final StringCacheEntry[] cache = new StringCacheEntry[CACHE_SIZE];
+        private final FastCacheEntry[] cache = new FastCacheEntry[CACHE_SIZE];
 
         /**
          * Get the string if it is stored.
@@ -138,7 +141,7 @@
          */
         String getString(int hash, long msb, long lsb, int offset) {
             int index = hash & (CACHE_SIZE - 1);
-            StringCacheEntry e = cache[index];
+            FastCacheEntry e = cache[index];
             if (e != null && e.matches(msb, lsb, offset)) {
                 return e.string;
             }
@@ -159,36 +162,23 @@
             return s.length() <= MAX_STRING_SIZE;
         }
 
-        void addString(int hash, StringCacheEntry entry) {
+        void addString(int hash, FastCacheEntry entry) {
             int index = hash & (CACHE_SIZE - 1);
             cache[index] = entry;
         }
 
     }
 
-    static class StringCacheEntry {
+    private static class StringCacheKey {
         private final int hash;
         private final long msb, lsb;
         private final int offset;
-        private String string;
 
-        StringCacheEntry(int hash, long msb, long lsb, int offset, String string) {
+        StringCacheKey(int hash, long msb, long lsb, int offset) {
             this.hash = hash;
             this.msb = msb;
             this.lsb = lsb;
             this.offset = offset;
-            this.string = string;
-        }
-
-        void setString(String string) {
-            if (string == null) {
-                throw new NullPointerException();
-            }
-            this.string = string;
-        }
-
-        boolean matches(long msb, long lsb, int offset) {
-            return this.offset == offset && this.msb == msb && this.lsb == lsb;
         }
 
         @Override
@@ -201,14 +191,14 @@
             if (other == this) {
                 return true;
             }
-            if (!(other instanceof StringCacheEntry)) {
+            if (!(other instanceof StringCacheKey)) {
                 return false;
             }
-            StringCacheEntry o = (StringCacheEntry) other;
+            StringCacheKey o = (StringCacheKey) other;
             return o.hash == hash && o.msb == msb && o.lsb == lsb &&
                     o.offset == offset;
         }
-        
+
         @Override
         public String toString() {
             StringBuilder buff = new StringBuilder();
@@ -220,4 +210,43 @@
 
     }
 
+    private static class FastCacheEntry {
+
+        private final int hash;
+        private final long msb, lsb;
+        private final int offset;
+        private final String string;
+
+        FastCacheEntry(int hash, long msb, long lsb, int offset, String string) {
+            this.hash = hash;
+            this.msb = msb;
+            this.lsb = lsb;
+            this.offset = offset;
+            this.string = string;
+        }
+
+        boolean matches(long msb, long lsb, int offset) {
+            return this.offset == offset && this.msb == msb && this.lsb == lsb;
+        }
+
+        @Override
+        public int hashCode() {
+            return hash;
+        }
+
+        @Override
+        public boolean equals(Object other) {
+            if (other == this) {
+                return true;
+            }
+            if (!(other instanceof FastCacheEntry)) {
+                return false;
+            }
+            FastCacheEntry o = (FastCacheEntry) other;
+            return o.hash == hash && o.msb == msb && o.lsb == lsb &&
+                    o.offset == offset;
+        }
+
+    }
+
 }
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