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From "kieran (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-436) [PATCH] TermInfosReader, SegmentTermEnum Out Of Memory Exception
Date Wed, 21 Sep 2005 15:41:27 GMT
[PATCH] TermInfosReader, SegmentTermEnum Out Of Memory Exception
----------------------------------------------------------------

         Key: LUCENE-436
         URL: http://issues.apache.org/jira/browse/LUCENE-436
     Project: Lucene - Java
        Type: Improvement
  Components: Index  
    Versions: 1.4    
 Environment: Solaris JVM 1.4.1
Linux JVM 1.4.2/1.5.0
Windows not tested
    Reporter: kieran


We've been experiencing terrible memory problems on our production search server, running
lucene (1.4.3).

Our live app regularly opens new indexes and, in doing so, releases old IndexReaders for garbage
collection.

But...there appears to be a memory leak in org.apache.lucene.index.TermInfosReader.java.
Under certain conditions (possibly related to JVM version, although I've personally observed
it under both linux JVM 1.4.2_06, and 1.5.0_03, and SUNOS JVM 1.4.1) the ThreadLocal member
variable, "enumerators" doesn't get garbage-collected when the TermInfosReader object is gc-ed.

Looking at the code in TermInfosReader.java, there's no reason why it _shouldn't_ be gc-ed,
so I can only presume (and I've seen this suggested elsewhere) that there could be a bug in
the garbage collector of some JVMs.

I've seen this problem briefly discussed; in particular at the following URL:
  http://java2.5341.com/msg/85821.html
The patch that Doug recommended, which is included in lucene-1.4.3 doesn't work in our particular
circumstances. Doug's patch only clears the ThreadLocal variable for the thread running the
finalizer (my knowledge of java breaks down here - I'm not sure which thread actually runs
the finalizer). In our situation, the TermInfosReader is (potentially) used by more than one
thread, meaning that Doug's patch _doesn't_ allow the affected JVMs to correctly collect garbage.

So...I've devised a simple patch which, from my observations on linux JVMs 1.4.2_06, and 1.5.0_03,
fixes this problem.

Kieran
PS Thanks to daniel naber for pointing me to jira/lucene

@@ -19,6 +19,7 @@
 import java.io.IOException;

 import org.apache.lucene.store.Directory;
+import java.util.Hashtable;

 /** This stores a monotonically increasing set of <Term, TermInfo> pairs in a
  * Directory.  Pairs are accessed either by Term or by ordinal position the
@@ -29,7 +30,7 @@
   private String segment;
   private FieldInfos fieldInfos;

-  private ThreadLocal enumerators = new ThreadLocal();
+  private final Hashtable enumeratorsByThread = new Hashtable();
   private SegmentTermEnum origEnum;
   private long size;

@@ -60,10 +61,10 @@
   }

   private SegmentTermEnum getEnum() {
-    SegmentTermEnum termEnum = (SegmentTermEnum)enumerators.get();
+    SegmentTermEnum termEnum = (SegmentTermEnum)enumeratorsByThread.get(Thread.currentThread());
     if (termEnum == null) {
       termEnum = terms();
-      enumerators.set(termEnum);
+      enumeratorsByThread.put(Thread.currentThread(), termEnum);
     }
     return termEnum;
   }
@@ -195,5 +196,15 @@
   public SegmentTermEnum terms(Term term) throws IOException {
     get(term);
     return (SegmentTermEnum)getEnum().clone();
+  }
+
+  /* some jvms might have trouble gc-ing enumeratorsByThread */
+  protected void finalize() throws Throwable {
+    try {
+        // make sure gc can clear up.
+        enumeratorsByThread.clear();
+    } finally {
+        super.finalize();
+    }
   }
 }



TermInfosReader.java, full source:
======================================
package org.apache.lucene.index;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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.io.IOException;

import org.apache.lucene.store.Directory;
import java.util.Hashtable;

/** This stores a monotonically increasing set of <Term, TermInfo> pairs in a
 * Directory.  Pairs are accessed either by Term or by ordinal position the
 * set.  */

final class TermInfosReader {
  private Directory directory;
  private String segment;
  private FieldInfos fieldInfos;

  private final Hashtable enumeratorsByThread = new Hashtable();
  private SegmentTermEnum origEnum;
  private long size;

  TermInfosReader(Directory dir, String seg, FieldInfos fis)
       throws IOException {
    directory = dir;
    segment = seg;
    fieldInfos = fis;

    origEnum = new SegmentTermEnum(directory.openFile(segment + ".tis"),
                                   fieldInfos, false);
    size = origEnum.size;
    readIndex();
  }

  public int getSkipInterval() {
    return origEnum.skipInterval;
  }

  final void close() throws IOException {
    if (origEnum != null)
      origEnum.close();
  }

  /** Returns the number of term/value pairs in the set. */
  final long size() {
    return size;
  }

  private SegmentTermEnum getEnum() {
    SegmentTermEnum termEnum = (SegmentTermEnum)enumeratorsByThread.get(Thread.currentThread());
    if (termEnum == null) {
      termEnum = terms();
      enumeratorsByThread.put(Thread.currentThread(), termEnum);
    }
    return termEnum;
  }

  Term[] indexTerms = null;
  TermInfo[] indexInfos;
  long[] indexPointers;

  private final void readIndex() throws IOException {
    SegmentTermEnum indexEnum =
      new SegmentTermEnum(directory.openFile(segment + ".tii"),
			  fieldInfos, true);
    try {
      int indexSize = (int)indexEnum.size;

      indexTerms = new Term[indexSize];
      indexInfos = new TermInfo[indexSize];
      indexPointers = new long[indexSize];

      for (int i = 0; indexEnum.next(); i++) {
	indexTerms[i] = indexEnum.term();
	indexInfos[i] = indexEnum.termInfo();
	indexPointers[i] = indexEnum.indexPointer;
      }
    } finally {
      indexEnum.close();
    }
  }

  /** Returns the offset of the greatest index entry which is less than or equal to term.*/
  private final int getIndexOffset(Term term) throws IOException {
    int lo = 0;					  // binary search indexTerms[]
    int hi = indexTerms.length - 1;

    while (hi >= lo) {
      int mid = (lo + hi) >> 1;
      int delta = term.compareTo(indexTerms[mid]);
      if (delta < 0)
	hi = mid - 1;
      else if (delta > 0)
	lo = mid + 1;
      else
	return mid;
    }
    return hi;
  }

  private final void seekEnum(int indexOffset) throws IOException {
    getEnum().seek(indexPointers[indexOffset],
	      (indexOffset * getEnum().indexInterval) - 1,
	      indexTerms[indexOffset], indexInfos[indexOffset]);
  }

  /** Returns the TermInfo for a Term in the set, or null. */
  TermInfo get(Term term) throws IOException {
    if (size == 0) return null;

    // optimize sequential access: first try scanning cached enum w/o seeking
    SegmentTermEnum enumerator = getEnum();
    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/enumerator.indexInterval)+1;
      if (indexTerms.length == enumOffset	  // but before end of block
	  || term.compareTo(indexTerms[enumOffset]) < 0)
	return scanEnum(term);			  // no need to seek
    }

    // 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();
    while (term.compareTo(enumerator.term()) > 0 && enumerator.next()) {}
    if (enumerator.term() != null && term.compareTo(enumerator.term()) == 0)
      return enumerator.termInfo();
    else
      return null;
  }

  /** Returns the nth term in the set. */
  final Term get(int position) throws IOException {
    if (size == 0) return null;

    SegmentTermEnum enumerator = getEnum();
    if (enumerator != null && enumerator.term() != null &&
        position >= enumerator.position &&
	position < (enumerator.position + enumerator.indexInterval))
      return scanEnum(position);		  // can avoid seek

    seekEnum(position / enumerator.indexInterval); // must seek
    return scanEnum(position);
  }

  private final Term scanEnum(int position) throws IOException {
    SegmentTermEnum enumerator = getEnum();
    while(enumerator.position < position)
      if (!enumerator.next())
	return null;

    return enumerator.term();
  }

  /** Returns the position of a Term in the set or -1. */
  final long getPosition(Term term) throws IOException {
    if (size == 0) return -1;

    int indexOffset = getIndexOffset(term);
    seekEnum(indexOffset);

    SegmentTermEnum enumerator = getEnum();
    while(term.compareTo(enumerator.term()) > 0 && enumerator.next()) {}

    if (term.compareTo(enumerator.term()) == 0)
      return enumerator.position;
    else
      return -1;
  }

  /** Returns an enumeration of all the Terms and TermInfos in the set. */
  public SegmentTermEnum terms() {
    return (SegmentTermEnum)origEnum.clone();
  }

  /** 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();
  }

  /* some jvms might have trouble gc-ing enumeratorsByThread */ 
  protected void finalize() throws Throwable {
    try {
        // make sure gc can clear up.
        enumeratorsByThread.clear();
    } finally {
        super.finalize();
    }
  }
}


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