Memory leak puzzle

Question

Hello guys,
I'm having a very, very difficult time debugging this memory leak on my server. I'm pretty sure it's related to berkeley DB XML, bu I just couldn't prove this in numbers.
My server: Debian GNU/Linux 2.4.27-2-386 #1 Wed Aug 17 09:33:35 UTC 2005 i686 GNU/Linux, 512 MB of RAM, Pentium 4-class processor.
Here's the behaviour. I start Tomcat 5.5.15, the application is loaded, current memory status:
delegaciainterativa:~# free -m
total used free shared buffers cached
Mem: 440 346 94 0 14 282
-/+ buffers/cache: 49 391
Swap: 909 4 905
So, I've got 94 MBs of free memory. Now, here's this JSP I'm running:
<%@ page language="java" %>
<%@ page session="true" %>
<%@ page import="br.gov.al.delegaciainterativa.admin.*"%>
<%@ page import="br.gov.al.delegaciainterativa.controles.*"%>
<%@ page import="br.gov.al.delegaciainterativa.admin.areas.*"%>
<%@ page import="br.gov.al.delegaciainterativa.controles.BdbXmlAmbiente"%>
<%@ page import="java.util.*"%>
<%@ page import="javax.servlet.RequestDispatcher"%>
<%@ page import="com.sleepycat.dbxml.XmlContainer"%>
<%@ page import="com.sleepycat.dbxml.XmlDocument"%>
<%@ page import="com.sleepycat.dbxml.XmlException"%>
<%@ page import="com.sleepycat.dbxml.XmlIndexDeclaration"%>
<%@ page import="com.sleepycat.dbxml.XmlIndexSpecification"%>
<%@ page import="com.sleepycat.dbxml.XmlQueryContext"%>
<%@ page import="com.sleepycat.dbxml.XmlQueryExpression"%>
<%@ page import="com.sleepycat.dbxml.XmlResults"%>
<%@ page import="com.sleepycat.dbxml.XmlTransaction"%>
<%@ page import="com.sleepycat.dbxml.XmlUpdateContext"%>
<%@ page import="com.sleepycat.dbxml.XmlValue"%>
<%@ page import="com.sleepycat.dbxml.XmlUpdateContext"%>
<%@ page import="com.sleepycat.dbxml.XmlQueryContext"%>
<%@ include file="config.jsp"%>
<%!
     final String _grupoPagina = "visualizaLogsUsuario";
%>
<font face="verdana" size="1">
<%
          HttpSession sessao = request.getSession(true);
          BdbXmlAmbiente bdbxmlAmbiente = new BdbXmlAmbiente();
          XmlContainer container = bdbxmlAmbiente.abrirContainer(Config.getNomeContainerBO());
          String fullquery = "";
          fullquery = "for $i in collection('"+ Config.getNomeContainerBO() +"')/BO \n";     
          fullquery += "where $i/cadastro/fim/data/date >= '2006-00-00' \n";
          fullquery += "return $i";
ArrayList docs = new ArrayList();
XmlResults results = null;
     XmlValue value = null;
     XmlDocument document = null;
try {
     XmlQueryContext context = bdbxmlAmbiente.getEnvironmentInit().getManager().createQueryContext();
     context.setEvaluationType(XmlQueryContext.Eager);
     XmlQueryExpression xqe = bdbxmlAmbiente.getEnvironmentInit().getManager().prepare(fullquery, context);
     results = xqe.execute(context);
               out.println("<p>fez busca, deletando...</p>");
while (results.hasNext()) {
     value = results.next();
document = value.asDocument();
     document.fetchAllData();
     out.println(document.getName() + "<br>");
//out.println("<p>total: " + results.size() + "</p>");
} catch (Throwable e) {
     out.println(e);
e.printStackTrace();
} finally {
               results.delete();
%>
This basically loads about 1600 small documents (~5KB) from the container, and guess how memory is now:
delegaciainterativa:~# free -m
total used free shared buffers cached
Mem: 440 429 11 0 14 282
-/+ buffers/cache: 132 308
Swap: 909 4 905
That's about 83Mbs consumed!! And if I perform other searches like this, this keeps eating up more and more memory, then swapping and getting slow... and sometimes crashing Tomcat.
Here's the big mistery: the memory NEVER GETS RELEASED. Even calling delete(), as I did explicitily, it doesnt release the memory. It keeps increasing as searches are performed.
Now, let's go to the profiler. I've installed JProfiler and run it on this server, and here're the results: http://freeunix.com.br/All_Objects.html
Even more puzzling, I havent got any impressive amount of memory consumption.
So, what can I do to figure this out? The only way to release memory is to restart the server once and a while, which far from ideal.
I'd really would appreciate any help about this, since I'm on production with this server.
cheers,
-- Breno Jacinto

Answer 1

Hello George,
    I tried this:
<%
          HttpSession sessao = request.getSession(true);
          BdbXmlAmbiente bdbxmlAmbiente = new BdbXmlAmbiente();
          XmlContainer container = bdbxmlAmbiente.abrirContainer(Config.getNomeContainerBO());
          String fullquery = "";
          fullquery = "for $i in collection('"+ Config.getNomeContainerBO() +"')/BO \n";     
          fullquery += "where $i/cadastro/fim/data/date >= '2006-00-00' \n";
          fullquery += "return $i";
        ArrayList docs = new ArrayList();
        XmlResults results = null;
         XmlValue value = null;
         XmlDocument document = null;
        try {
             XmlQueryContext context = bdbxmlAmbiente.getEnvironmentInit().getManager().createQueryContext();
             context.setEvaluationType(XmlQueryContext.Eager);
             XmlQueryExpression xqe = bdbxmlAmbiente.getEnvironmentInit().getManager().prepare(fullquery, context);
             results = xqe.execute(context);
               out.println("<p>fez busca, deletando...</p>");
            while (results.hasNext()) {
                 value = results.next();
                document = value.asDocument();
                    document.fetchAllData();
                    out.println(document.getName() + "<br>");
                    value.delete();
                    document.delete();
            //out.println("<p>total: " + results.size() + "</p>");
               context.delete();
               xqe.delete();
               results.delete();
        } catch (Throwable e) {
             out.println(e);
            e.printStackTrace();
%>
     Don't you think that it's too much to consume ~80 MBs of RAM, in a search that returns ~1600 5 KB  documents? And worse, this amount is never released.
     I'm wondering if there's any configuration issue here? Such as JVM's Heap size, or BDBXML Environment Initialization?
thanks,
-- Breno