Index: MoreLikeThis.java
===================================================================
--- MoreLikeThis.java	(revision 798477)
+++ MoreLikeThis.java	(working copy)
@@ -36,6 +36,8 @@
 import java.util.Set;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.WeakHashMap;
+import java.util.LinkedHashMap;
 import java.util.Collection;
 import java.util.Iterator;
 import java.io.IOException;
@@ -287,6 +289,16 @@
     private float boostFactor = 1;
 
     /**
+     * Cache term frequencies for recently accessed terms
+     */
+    private WeakHashMap termFreqCache = null;
+    
+    /**
+     * Term cache size
+     */
+    private int termFreqCacheSize = 0;
+    
+    /**
      * Returns the boost factor used when boosting terms
      * @return the boost factor used when boosting terms
      */
@@ -301,6 +313,14 @@
     public void setBoostFactor(float boostFactor) {
         this.boostFactor = boostFactor;
     }
+    
+    /**
+     * Sets the boost factor to use when boosting terms
+     * @param boostFactor
+     */
+    public void setTermCacheSize(int size) {
+        this.termFreqCacheSize = size;
+    }
 
     /**
      * Constructor requiring an IndexReader.
@@ -310,9 +330,22 @@
     }
 
     public MoreLikeThis(IndexReader ir, Similarity sim){
-      this.ir = ir;
-      this.similarity = sim;
+      this(ir, sim, 1000);
     }
+    
+	public MoreLikeThis(IndexReader ir, int termCacheSize ){
+		this(ir, new DefaultSimilarity(), termCacheSize);
+	}
+	
+    public MoreLikeThis(IndexReader ir, Similarity sim, int termCacheSize ){
+        this.termFreqCacheSize = termCacheSize;
+        this.ir = ir;
+        this.similarity = sim;
+        termFreqCache = new WeakHashMap();
+		LRULinkedHashMap fields = new LRULinkedHashMap(termCacheSize+1, 0.75f, true);
+		fields.setMaxTerms(termCacheSize);
+        termFreqCache.put(ir, fields);
+    }
 
 
   public Similarity getSimilarity() {
@@ -648,8 +681,10 @@
             // go through all the fields and find the largest document frequency
             String topField = fieldNames[0];
             int docFreq = 0;
+            Map cache = (Map)this.termFreqCache.get(this.ir);
             for (int i = 0; i < fieldNames.length; i++) {
-                int freq = ir.docFreq(new Term(fieldNames[i], word));
+                
+                int freq = this.getTermFrequency( cache, word, fieldNames[i] );
                 topField = (freq > docFreq) ? fieldNames[i] : topField;
                 docFreq = (freq > docFreq) ? freq : docFreq;
             }
@@ -678,6 +713,35 @@
     }
 
     /**
+     * Fetches term frequency from the index, via the LRU cache
+     */
+    private int getTermFrequency( Map cache, String term, String field ) throws IOException
+    {
+        // get the field cache
+        Map fieldCache = (Map)cache.get(field);
+        int freq = 0;
+        
+        if ( fieldCache == null ) {
+            fieldCache = new HashMap();
+            fieldCache.put(term,new Integer(freq));
+            cache.put( field, fieldCache );
+            freq = ir.docFreq(new Term(field, term));
+        }
+        else {
+            Integer intbox = (Integer)fieldCache.get(term);
+            if ( intbox != null )
+            {
+                freq = intbox.intValue();
+            }
+            else
+            {
+                fieldCache.put(term,new Integer(freq));
+            }
+        }
+        return freq;
+    }
+    
+    /**
      * Describe the parameters that control how the "more like this" query is formed.
      */
     public String describeParams() {
@@ -973,5 +1037,20 @@
         }
     }
     
+    protected class LRULinkedHashMap extends LinkedHashMap
+    {
+        public LRULinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) {
+            super(initialCapacity, loadFactor, accessOrder);
+        }
+        private int MAX_TERMS = 0;
+        public void setMaxTerms(int terms) {
+            MAX_TERMS = terms;
+        }
+        public boolean removeEldestEntry(Map.Entry eldest) {
+            return size() > MAX_TERMS;
+        }
+    }
     
 }
+
+
Index: MoreLikeThisQuery.java
===================================================================
--- MoreLikeThisQuery.java	(revision 798477)
+++ MoreLikeThisQuery.java	(working copy)
@@ -43,6 +43,7 @@
     private String likeText;
     private String[] moreLikeFields;
     private Analyzer analyzer;
+    private int termCacheSize = -1;
     float percentTermsToMatch=0.3f;
     int minTermFrequency=1;
     int maxQueryTerms=5;
@@ -55,15 +56,20 @@
      */
     public MoreLikeThisQuery(String likeText, String[] moreLikeFields, Analyzer analyzer)
     {
+        this(likeText, moreLikeFields, analyzer, -1 );
+    }
+    public MoreLikeThisQuery(String likeText, String[] moreLikeFields, Analyzer analyzer, int termCacheSize )
+    {
         this.likeText=likeText;
         this.moreLikeFields=moreLikeFields;
         this.analyzer=analyzer;
+        this.termCacheSize=termCacheSize;
     }
     
     public Query rewrite(IndexReader reader) throws IOException
     {
         MoreLikeThis mlt=new MoreLikeThis(reader);
-        
+        if ( this.termCacheSize > -1 ) mlt.setTermCacheSize(this.termCacheSize);
         mlt.setFieldNames(moreLikeFields);
         mlt.setAnalyzer(analyzer);
         mlt.setMinTermFreq(minTermFrequency);