LUCENE-1195: Improve term lookup performance by adding a LRU cache to the TermInfosReader.

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@659602 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -183,6 +183,11 @@ Optimizations
  5. LUCENE-1183: Optimized TRStringDistance class (in contrib/spell) that uses
     less memory than the previous version.  (Cédrik LIME via Otis Gospodnetic)
 
+ 6. LUCENE-1195: Improve term lookup performance by adding a LRU cache to the
+    TermInfosReader. In performance experiments the speedup was about 25% on 
+    average on mid-size indexes with ~500,000 documents for queries with 3 
+    terms and about 7% on larger indexes with ~4.3M documents. (Michael Busch)
+
 Documentation
 
   1. LUCENE-1236:  Added some clarifying remarks to EdgeNGram*.java (Hiroaki Kawai via Grant Ingersoll)

src/java/org/apache/lucene/index/SegmentTermEnum.java

@@ -150,10 +150,15 @@ final class SegmentTermEnum extends TermEnum implements Cloneable {
     return true;
   }
 
-  /** Optimized scan, without allocating new terms. */
-  final void scanTo(Term term) throws IOException {
+  /** Optimized scan, without allocating new terms. 
+   *  Return number of invocations to next(). */
+  final int scanTo(Term term) throws IOException {
     scanBuffer.set(term);
-    while (scanBuffer.compareTo(termBuffer) > 0 && next()) {}
+    int count = 0;
+    while (scanBuffer.compareTo(termBuffer) > 0 && next()) {
+      count++;
+    }
+    return count;
   }
 
   /** Returns the current Term in the enumeration.

src/java/org/apache/lucene/index/TermInfosReader.java

@@ -21,6 +21,8 @@ import java.io.IOException;
 
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.BufferedIndexInput;
+import org.apache.lucene.util.cache.Cache;
+import org.apache.lucene.util.cache.SimpleLRUCache;
 
 /** This stores a monotonically increasing set of <Term, TermInfo> pairs in a
  * Directory.  Pairs are accessed either by Term or by ordinal position the
@@ -31,7 +33,7 @@ final class TermInfosReader {
   private String segment;
   private FieldInfos fieldInfos;
 
-  private ThreadLocal enumerators = new ThreadLocal();
+  private ThreadLocal threadResources = new ThreadLocal();
   private SegmentTermEnum origEnum;
   private long size;
 
@@ -44,6 +46,18 @@ final class TermInfosReader {
   private int indexDivisor = 1;
   private int totalIndexInterval;
 
+  private final static int DEFAULT_CACHE_SIZE = 1024;
+  
+  /**
+   * Per-thread resources managed by ThreadLocal
+   */
+  private static final class ThreadResources {
+    SegmentTermEnum termEnum;
+    
+    // Used for caching the least recently looked-up Terms
+    Cache termInfoCache;
+  }
+  
   TermInfosReader(Directory dir, String seg, FieldInfos fis)
        throws CorruptIndexException, IOException {
     this(dir, seg, fis, BufferedIndexInput.BUFFER_SIZE);
@@ -129,7 +143,7 @@ final class TermInfosReader {
       origEnum.close();
     if (indexEnum != null)
       indexEnum.close();
-    enumerators.set(null);
+    threadResources.set(null);
   }
 
   /** Returns the number of term/value pairs in the set. */
@@ -137,13 +151,16 @@ final class TermInfosReader {
     return size;
   }
 
-  private SegmentTermEnum getEnum() {
-    SegmentTermEnum termEnum = (SegmentTermEnum)enumerators.get();
-    if (termEnum == null) {
-      termEnum = terms();
-      enumerators.set(termEnum);
+  private ThreadResources getThreadResources() {
+    ThreadResources resources = (ThreadResources)threadResources.get();
+    if (resources == null) {
+      resources = new ThreadResources();
+      resources.termEnum = terms();
+      // Cache does not have to be thread-safe, it is only used by one thread at the same time
+      resources.termInfoCache = new SimpleLRUCache(DEFAULT_CACHE_SIZE);
+      threadResources.set(resources);
     }
-    return termEnum;
+    return resources;
   }
 
   private synchronized void ensureIndexIsRead() throws IOException {
@@ -189,60 +206,94 @@ final class TermInfosReader {
     return hi;
   }
 
-  private final void seekEnum(int indexOffset) throws IOException {
-    getEnum().seek(indexPointers[indexOffset],
+  private final void seekEnum(SegmentTermEnum enumerator, int indexOffset) throws IOException {
+    enumerator.seek(indexPointers[indexOffset],
                    (indexOffset * totalIndexInterval) - 1,
                    indexTerms[indexOffset], indexInfos[indexOffset]);
   }
 
   /** Returns the TermInfo for a Term in the set, or null. */
   TermInfo get(Term term) throws IOException {
+    return get(term, true);
+  }
+  
+  /** Returns the TermInfo for a Term in the set, or null. */
+  private TermInfo get(Term term, boolean useCache) throws IOException {
     if (size == 0) return null;
 
     ensureIndexIsRead();
-
+    
+    TermInfo ti;
+    ThreadResources resources = getThreadResources();
+    Cache cache = null;
+    
+    if (useCache) {
+      cache = resources.termInfoCache;
+      // check the cache first if the term was recently looked up
+      ti = (TermInfo) cache.get(term);
+      if (ti != null) {
+        return ti;
+      }
+    }
+    
     // optimize sequential access: first try scanning cached enum w/o seeking
-    SegmentTermEnum enumerator = getEnum();
+    SegmentTermEnum enumerator = resources.termEnum;
     if (enumerator.term() != null                 // term is at or past current
 	&& ((enumerator.prev() != null && term.compareTo(enumerator.prev())> 0)
 	    || term.compareTo(enumerator.term()) >= 0)) {
       int enumOffset = (int)(enumerator.position/totalIndexInterval)+1;
       if (indexTerms.length == enumOffset	  // but before end of block
-	  || term.compareTo(indexTerms[enumOffset]) < 0)
-	return scanEnum(term);			  // no need to seek
+    || term.compareTo(indexTerms[enumOffset]) < 0) {
+       // no need to seek
+
+        int numScans = enumerator.scanTo(term);
+        if (enumerator.term() != null && term.compareTo(enumerator.term()) == 0) {
+          ti = enumerator.termInfo();
+          if (cache != null && numScans > 1) {
+            // we only  want to put this TermInfo into the cache if
+            // scanEnum skipped more than one dictionary entry.
+            // This prevents RangeQueries or WildcardQueries to 
+            // wipe out the cache when they iterate over a large numbers
+            // of terms in order
+            cache.put(term, ti);
+          }
+        } else {
+          ti = null;
+        }
+
+        return ti;
+      }  
     }
 
     // random-access: must seek
-    seekEnum(getIndexOffset(term));
-    return scanEnum(term);
-  }
-
-  /** Scans within block for matching term. */
-  private final TermInfo scanEnum(Term term) throws IOException {
-    SegmentTermEnum enumerator = getEnum();
+    seekEnum(enumerator, getIndexOffset(term));
     enumerator.scanTo(term);
-    if (enumerator.term() != null && term.compareTo(enumerator.term()) == 0)
-      return enumerator.termInfo();
-    else
-      return null;
+    if (enumerator.term() != null && term.compareTo(enumerator.term()) == 0) {
+      ti = enumerator.termInfo();
+      if (cache != null) {
+        cache.put(term, ti);
+      }
+    } else {
+      ti = null;
+    }
+    return ti;
   }
 
   /** Returns the nth term in the set. */
   final Term get(int position) throws IOException {
     if (size == 0) return null;
 
-    SegmentTermEnum enumerator = getEnum();
+    SegmentTermEnum enumerator = getThreadResources().termEnum;
     if (enumerator != null && enumerator.term() != null &&
         position >= enumerator.position &&
 	position < (enumerator.position + totalIndexInterval))
-      return scanEnum(position);		  // can avoid seek
+      return scanEnum(enumerator, position);      // can avoid seek
 
-    seekEnum(position/totalIndexInterval); // must seek
-    return scanEnum(position);
+    seekEnum(enumerator, position/totalIndexInterval); // must seek
+    return scanEnum(enumerator, position);
   }
 
-  private final Term scanEnum(int position) throws IOException {
-    SegmentTermEnum enumerator = getEnum();
+  private final Term scanEnum(SegmentTermEnum enumerator, int position) throws IOException {
     while(enumerator.position < position)
       if (!enumerator.next())
 	return null;
@@ -256,9 +307,10 @@ final class TermInfosReader {
 
     ensureIndexIsRead();
     int indexOffset = getIndexOffset(term);
-    seekEnum(indexOffset);
+    
+    SegmentTermEnum enumerator = getThreadResources().termEnum;
+    seekEnum(enumerator, indexOffset);
 
-    SegmentTermEnum enumerator = getEnum();
     while(term.compareTo(enumerator.term()) > 0 && enumerator.next()) {}
 
     if (term.compareTo(enumerator.term()) == 0)
@@ -274,7 +326,9 @@ final class TermInfosReader {
 
   /** Returns an enumeration of terms starting at or after the named term. */
   public SegmentTermEnum terms(Term term) throws IOException {
-    get(term);
-    return (SegmentTermEnum)getEnum().clone();
+    // don't use the cache in this call because we want to reposition the
+    // enumeration
+    get(term, false);
+    return (SegmentTermEnum)getThreadResources().termEnum.clone();
   }
 }

src/java/org/apache/lucene/util/cache/Cache.java

@@ -0,0 +1,100 @@
+package org.apache.lucene.util.cache;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+/**
+ * Base class for cache implementations.
+ */
+public abstract class Cache {
+  
+  /**
+   * Simple Cache wrapper that synchronizes all
+   * calls that access the cache. 
+   */
+  static class SynchronizedCache extends Cache {
+    Object mutex;
+    Cache  cache;
+    
+    SynchronizedCache(Cache cache) {
+      this.cache = cache;
+      this.mutex = this;
+    }
+    
+    SynchronizedCache(Cache cache, Object mutex) {
+      this.cache = cache;
+      this.mutex = mutex;
+    }
+    
+    public void put(Object key, Object value) {
+      synchronized(mutex) {cache.put(key, value);}
+    }
+    
+    public Object get(Object key) {
+      synchronized(mutex) {return cache.get(key);}
+    }
+    
+    public boolean containsKey(Object key) {
+      synchronized(mutex) {return cache.containsKey(key);}
+    }
+    
+    public void close() {
+      synchronized(mutex) {cache.close();}
+    }
+    
+    Cache getSynchronizedCache() {
+      return this;
+    }
+  }
+  
+  public static Cache synchronizedCache(Cache cache) {
+    return cache.getSynchronizedCache();
+  }
+
+  /**
+   * Called by {@link #synchronizedCache(Cache)}. This method
+   * returns a {@link SynchronizedCache} instance that wraps
+   * this instance by default and can be overridden to return
+   * e. g. subclasses of {@link SynchronizedCache} or this
+   * in case this cache is already synchronized.
+   */
+  Cache getSynchronizedCache() {
+    return new SynchronizedCache(this);
+  }
+  
+  /**
+   * Puts a (key, value)-pair into the cache. 
+   */
+  public abstract void put(Object key, Object value);
+  
+  /**
+   * Returns the value for the given key. 
+   */
+  public abstract Object get(Object key);
+  
+  /**
+   * Returns whether the given key is in this cache. 
+   */
+  public abstract boolean containsKey(Object key);
+  
+  /**
+   * Closes the cache.
+   */
+  public abstract void close();
+  
+}

src/java/org/apache/lucene/util/cache/SimpleLRUCache.java

@@ -0,0 +1,49 @@
+package org.apache.lucene.util.cache;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Simple LRU cache implementation that uses a LinkedHashMap.
+ * This cache is not synchronized, use {@link Cache#synchronizedCache(Cache)}
+ * if needed.
+ * 
+ */
+public class SimpleLRUCache extends SimpleMapCache {
+  private final static float LOADFACTOR = 0.75f;
+
+  private int cacheSize;
+
+  /**
+   * Creates a last-recently-used cache with the specified size. 
+   */
+  public SimpleLRUCache(int cacheSize) {
+    super(null);
+    this.cacheSize = cacheSize;
+    int capacity = (int) Math.ceil(cacheSize / LOADFACTOR) + 1;
+
+    super.map = new LinkedHashMap(capacity, LOADFACTOR, true) {
+      protected boolean removeEldestEntry(Map.Entry eldest) {
+        return size() > SimpleLRUCache.this.cacheSize;
+      }
+    };
+  }
+
+}

src/java/org/apache/lucene/util/cache/SimpleMapCache.java

@@ -0,0 +1,100 @@
+package org.apache.lucene.util.cache;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Simple cache implementation that uses a HashMap to store (key, value) pairs.
+ * This cache is not synchronized, use {@link Cache#synchronizedCache(Cache)}
+ * if needed.
+ */
+public class SimpleMapCache extends Cache {
+  Map map;
+  
+  public SimpleMapCache() {
+    this(new HashMap());
+  }
+
+  public SimpleMapCache(Map map) {
+    this.map = map;
+  }
+  
+  public Object get(Object key) {
+    return map.get(key);
+  }
+
+  public void put(Object key, Object value) {
+    map.put(key, value);
+  }
+
+  public void close() {
+    // NOOP
+  }
+
+  public boolean containsKey(Object key) {
+    return map.containsKey(key);
+  }
+  
+  /**
+   * Returns a Set containing all keys in this cache.
+   */
+  public Set keySet() {
+    return map.keySet();
+  }
+  
+  Cache getSynchronizedCache() {
+    return new SynchronizedSimpleMapCache(this);
+  }
+  
+  private static class SynchronizedSimpleMapCache extends SimpleMapCache {
+    Object mutex;
+    SimpleMapCache cache;
+    
+    SynchronizedSimpleMapCache(SimpleMapCache cache) {
+        this.cache = cache;
+        this.mutex = this;
+    }
+    
+    public void put(Object key, Object value) {
+        synchronized(mutex) {cache.put(key, value);}
+    }
+    
+    public Object get(Object key) {
+        synchronized(mutex) {return cache.get(key);}
+    }
+    
+    public boolean containsKey(Object key) {
+        synchronized(mutex) {return cache.containsKey(key);}
+    }
+    
+    public void close() {
+        synchronized(mutex) {cache.close();}
+    }
+    
+    public Set keySet() {
+      synchronized(mutex) {return cache.keySet();}
+    }
+    
+    Cache getSynchronizedCache() {
+      return this;
+    }
+  }
+}

src/test/org/apache/lucene/util/cache/TestSimpleLRUCache.java

@@ -0,0 +1,63 @@
+package org.apache.lucene.util.cache;
+
+/**
+* Licensed to the Apache Software Foundation (ASF) under one or more
+* contributor license agreements.  See the NOTICE file distributed with
+* this work for additional information regarding copyright ownership.
+* The ASF licenses this file to You under the Apache License, Version 2.0
+* (the "License"); you may not use this file except in compliance with
+* the License.  You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+import junit.framework.TestCase;
+
+public class TestSimpleLRUCache extends TestCase {
+
+  public void testLRUCache() throws Exception {
+    final int n = 100;
+    Object dummy = new Object();
+    
+    Cache cache = new SimpleLRUCache(n);
+    
+    for (int i = 0; i < n; i++) {
+      cache.put(new Integer(i), dummy);
+    }
+    
+    // access every 2nd item in cache
+    for (int i = 0; i < n; i+=2) {
+      assertNotNull(cache.get(new Integer(i)));
+    }
+    
+    // add n/2 elements to cache, the ones that weren't
+    // touched in the previous loop should now be thrown away
+    for (int i = n; i < n + (n / 2); i++) {
+      cache.put(new Integer(i), dummy);
+    }
+    
+    // access every 4th item in cache
+    for (int i = 0; i < n; i+=4) {
+      assertNotNull(cache.get(new Integer(i)));
+    }
+
+    // add 3/4n elements to cache, the ones that weren't
+    // touched in the previous loops should now be thrown away
+    for (int i = n; i < n + (n * 3 / 4); i++) {
+      cache.put(new Integer(i), dummy);
+    }
+    
+    // access every 4th item in cache
+    for (int i = 0; i < n; i+=4) {
+      assertNotNull(cache.get(new Integer(i)));
+    }
+    
+  }
+  
+}