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Date: Wed, 11 Jun 2008 11:16:45 -0700 (PDT)
From: "Ethan Tao (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Created: (LUCENE-1304) Memory Leak when using Custom Sort
 (i.e., DistanceSortSource) of LocalLucene with Lucene
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Memory Leak when using Custom Sort (i.e., DistanceSortSource) of LocalLucene with Lucene
----------------------------------------------------------------------------------------

                 Key: LUCENE-1304
                 URL: https://issues.apache.org/jira/browse/LUCENE-1304
             Project: Lucene - Java
          Issue Type: Bug
          Components: Search
    Affects Versions: 2.3
         Environment: Windows/JDK 1.6
            Reporter: Ethan Tao


We had the memory leak issue when using DistanceSortSource of LocalLucene for repeated query/search. In about 450 queries, we are experiencing out of memory error. After dig in the code, we found the problem source is coming from Lucene package, the way how it handles "custom" type comparator. Lucene internally caches all created comparators. In the case of query using LocalLucene, we create new comparator for every search due to different lon/lat and query terms. This causes major memory leak as the cached comparators are also holding memory for other large objects (e.g., bit sets). The solution we came up with: ( the proposed change from Lucene is 1 and 3 below)

1.	In Lucene package, create new file SortComparatorSourceUncacheable.java:

package org.apache.lucene.search;

import org.apache.lucene.index.IndexReader;
import java.io.IOException;
import java.io.Serializable;

public interface SortComparatorSourceUncacheable extends Serializable {
}

2.	Have your custom sort class to implement the interface

public class LocalSortSource extends DistanceSortSource implements SortComparatorSourceUncacheable {
...
}

3.	Modify Lucene's FieldSorterHitQueue.java to bypass caching for custom sort comparator:

Index: FieldSortedHitQueue.java
===================================================================
--- FieldSortedHitQueue.java     (revision 654583)
+++ FieldSortedHitQueue.java  (working copy)
@@ -53,7 +53,12 @@
     this.fields = new SortField[n];
     for (int i=0; i<n; ++i) {
       String fieldname = fields[i].getField();
-      comparators[i] = getCachedComparator (reader, fieldname, fields[i].getType(), fields[i].getLocale(), fields[i].getFactory());
+
+      if(fields[i].getFactory() instanceof SortComparatorSourceUncacheable) { // no caching to avoid memory leak
+        comparators[i] = getComparator (reader, fieldname, fields[i].getType(), fields[i].getLocale(), fields[i].getFactory());
+      } else {
+        comparators[i] = getCachedComparator (reader, fieldname, fields[i].getType(), fields[i].getLocale(), fields[i].getFactory());
+      }
       
       if (comparators[i].sortType() == SortField.STRING) {
                  this.fields[i] = new SortField (fieldname, fields[i].getLocale(), fields[i].getReverse());
@@ -157,7 +162,18 @@
   SortField[] getFields() {
     return fields;
   }
-  
+
+  static ScoreDocComparator getComparator (IndexReader reader, String field, int type, Locale locale, SortComparatorSource factory)
+    throws IOException {
+      if (type == SortField.DOC) return ScoreDocComparator.INDEXORDER;
+      if (type == SortField.SCORE) return ScoreDocComparator.RELEVANCE;
+      FieldCacheImpl.Entry entry = (factory != null)
+        ? new FieldCacheImpl.Entry (field, factory)
+        : new FieldCacheImpl.Entry (field, type, locale);
+      return (ScoreDocComparator)Comparators.createValue(reader, entry);
+    }
+
+

Otis suggests that I put this in Jira. I 'll attach a patch shortly for review. 

-Ethan


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