Creating and destroying threads is one of the worst performing operations, and should be avoided at ALMOST all costs.
I do not see this problem in my server impl of Lucene, internally multithreaded, and accessed via multiple threads from a Tomcat server. I have to assume many (most?) users of Lucene are doing so in a multithreaded server environment. I reviewed the bugs in java.sun related to memory leaks with ThreadLocal's. I don't think any of them apply in this case. Maybe you could provide a simplified ThreadLocal testcase that demonstrates the 'out of memory' condition? Are you sure that you do not have a modified version of Lucene that is somehow maintain a reference back to the ThreadLocal from the ThreadLocal's value, as this is a known JDK issue http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6254531 I don't see this bug as being applicable to the 1.9.1 or 1.4.3 code. Did you try running your server using 1.4.3? (our server code is based off the 1.4.3 codeset at this time). -----Original Message----- From: Andy Hind [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 22, 2006 12:48 PM To: java-dev@lucene.apache.org; [EMAIL PROTECTED] Subject: RE: [jira] Created: (LUCENE-529) TermInfosReader and other + instance ThreadLocal => transient/odd memory leaks => OutOfMemoryException For every IndexReader that is opened - there is one SegmentReader for every segment in the index - with its thread local - for each of these there is a TermInfosReader + its thread local. So I get 2 * (no of index segments) thread locals. I am creating index readers for a main index and transactional updates and layering the two. At the moment this is an issue, under stress testing, using tomcat, with thread pooling, with a pretty big changing index, left running for a few hours, it blows up. Thread locals are also used in other areas of the app. It would be better if threads were created and destroyed! It is certainly not insignificant for me and gives a JVM that creeps up in size pretty steadily over time. I have fixed this issue locally in the code and it works. Regards Andy -----Original Message----- From: Robert Engels [mailto:[EMAIL PROTECTED] Sent: 22 March 2006 17:46 To: java-dev@lucene.apache.org Subject: RE: [jira] Created: (LUCENE-529) TermInfosReader and other + instance ThreadLocal => transient/odd memory leaks => OutOfMemoryException There was a small mistake - there is a single TermInfoReader per segment. -----Original Message----- From: Robert Engels [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 22, 2006 11:37 AM To: java-dev@lucene.apache.org Subject: RE: [jira] Created: (LUCENE-529) TermInfosReader and other + instance ThreadLocal => transient/odd memory leaks => OutOfMemoryException There is only a single TermInfoReader per index. In order to share this instance with multiple threads, and avoid the overhead of creating new enumerators for each request, the enumerator for the thread is stored in a thread local. Normally, in a server application, threads are pooled, so new threads are not constantly created and destroyed, so the memory leak is insiginificant. The same reasoning holds true for the SegmentReader class. -----Original Message----- From: Andy Hind (JIRA) [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 22, 2006 11:07 AM To: java-dev@lucene.apache.org Subject: [jira] Created: (LUCENE-529) TermInfosReader and other + instance ThreadLocal => transient/odd memory leaks => OutOfMemoryException TermInfosReader and other + instance ThreadLocal => transient/odd memory leaks => OutOfMemoryException ------------------------------------------------------------------------ -------------------------------- Key: LUCENE-529 URL: http://issues.apache.org/jira/browse/LUCENE-529 Project: Lucene - Java Type: Bug Components: Index Versions: 1.9 Environment: Lucene 1.4.3 with 1.5.0_04 JVM or newer......will aplpy to 1.9 code Reporter: Andy Hind TermInfosReader uses an instance level ThreadLocal for enumerators. This is a transient/odd memory leak in lucene 1.4.3-1.9 and applies to current JVMs, not just an old JVM issue as described in the finalizer of the 1.9 code. There is also an instance level thread local in SegmentReader....which will have the same issue. There may be other uses which also need to be fixed. I don't understand the intended use for these variables.....however Each ThreadLocal has its own hashcode used for look up, see the ThreadLocal source code. Each instance of TermInfosReader will be creating an instance of the thread local. All this does is create an instance variable on each thread when it accesses the thread local. Setting it to null in the finaliser will set it to null on one thread, the finalizer thread, where it has never been created. There is no point to this :-( I assume there is a good concurrency reason why an instance variable can not be used... I have not used multi-threaded searching, but I have used a lot of threads each making searchers and searching. 1.4.3 has a clear memory leak caused by this thread local. This use case above is definitely solved by setting the thread local to null in the close(). This at least has a chance of being on the correct thread :-) I know reusing Searchers would help but that is my choice and I will get to that later .... Now you wnat to know why.... Thread locals are stored in a table of entries. Each entry is *weak reference* to the key (Here the TermInfosReader instance) and a *simple reference* to the thread local value. When the instance is GCed its key becomes null. This is now a stale entry in the table. Stale entries are cleared up in an ad hoc way and until they are cleared up the value will not be garbage collected. Until the instance is GCed it is a valid key and its presence may cause the table to expand. See the ThreadLocal code. So if you have lots of threads, all creating thread locals rapidly, you can get each thread holding a large table of thread locals which all contain many stale entries and preventing some objects from being garbage collected. The limited GC of the thread local table is not enough to save you from running out of memory. Summary: ======== - remove finalizer() - set the thread local to null in close() - values will be available for gc -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
