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https://issues.apache.org/jira/browse/CURATOR-167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14216788#comment-14216788
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Cameron McKenzie commented on CURATOR-167:
------------------------------------------
Looking briefly at the code, it would seem that this is probably just because
the NamespaceWatcherMap is holding references to all of the Watcher references
that are created by the NodeCache (which being an inner class will hold a
reference to the NodeCache itself). This means that a bunch of objects are not
going to be cleaned up the GC. I'm not sure what the solution is though. Maybe
the NodeCache needs to keep track of all of its Watcher references and ask for
them to be removed from the NamespaceWatcherMap when it closes. The
NamespaceWatcherMap is hidden under a few layers of abstraction though, so it's
not going to be very clean!
> Memory leak in NodeCache
> ------------------------
>
> Key: CURATOR-167
> URL: https://issues.apache.org/jira/browse/CURATOR-167
> Project: Apache Curator
> Issue Type: Bug
> Components: Client
> Affects Versions: 2.6.0
> Environment: Linux 3.13.0-37-generic #64~precise1-Ubuntu SMP Wed Sep
> 24 21:39:43 UTC 2014 i686 i686 i386 GNU/Linux
> java version "1.7.0_13"
> Java(TM) SE Runtime Environment (build 1.7.0_13-b20)
> Java HotSpot(TM) Server VM (build 23.7-b01, mixed mode)
> Reporter: Craig McNally
> Assignee: Scott Blum
> Priority: Critical
> Labels: heap, memory-leak, node-cache
> Attachments: heap.png, yourKit_NodeCacheMemoryLeakTest.png
>
>
> There's a memory leak in NodeCache. I was able to reliably reproduce the
> problem using a very simple test that performs the following:
> 1) Creates a CuratorFramework instance and starts it.
> 2) in a loop: Creates a NodeCache and starts it, then closes it.
> Eventually you get a java.lang.OutOfMemoryError: Java heap space. This
> happens regardless of the heap size, though it happens much faster with a
> small heap.
> Upon furher investigation w/ a profiler, I can see that each NodeCache is
> being referenced by the NamespaceWatcherMap.
> Here's the test code:
> {code:title=NodeCacheLeakTest.java|borderStyle=solid}
> import java.util.Date;
> import org.apache.curator.framework.CuratorFramework;
> import org.apache.curator.framework.CuratorFrameworkFactory;
> import org.apache.curator.framework.recipes.cache.NodeCache;
> import org.apache.curator.retry.ExponentialBackoffRetry;
> public class NodeCacheLeakTest {
> public static void main(String[] args) throws Exception {
> String zkConnect;
> if (args.length > 0 && args[0] != null)
> zkConnect = args[0];
> else
> zkConnect = "localhost:2181/test";
> CuratorFramework curator =
> CuratorFrameworkFactory.newClient(zkConnect,
> new ExponentialBackoffRetry(500, 10));
> curator.start();
> int count = 0;
> while (true) {
> String nodePath = "/foo/node-" + (count);
> NodeCache cache = new NodeCache(curator, nodePath);
> cache.start(true);
> cache.close();
> count++;
> if (count % 1000 == 0)
> System.out.println(new Date() + " Started and
> Closed " + count
> + " NodeCache instances");
> }
> }
> }
> {code}
> And here's the output/OOM Error when using (-Xms10m -Xmx10m -XX:+UseG1GC):
> {noformat}
> log4j:WARN No appenders could be found for logger
> (org.apache.curator.framework.imps.CuratorFrameworkImpl).
> log4j:WARN Please initialize the log4j system properly.
> log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more
> info.
> Tue Nov 18 15:59:12 GMT+00:00 2014 Started and Closed 1000 NodeCache instances
> Tue Nov 18 15:59:16 GMT+00:00 2014 Started and Closed 2000 NodeCache instances
> Tue Nov 18 15:59:20 GMT+00:00 2014 Started and Closed 3000 NodeCache instances
> Tue Nov 18 15:59:23 GMT+00:00 2014 Started and Closed 4000 NodeCache instances
> Tue Nov 18 15:59:27 GMT+00:00 2014 Started and Closed 5000 NodeCache instances
> Tue Nov 18 15:59:31 GMT+00:00 2014 Started and Closed 6000 NodeCache instances
> Tue Nov 18 15:59:36 GMT+00:00 2014 Started and Closed 7000 NodeCache instances
> Tue Nov 18 15:59:40 GMT+00:00 2014 Started and Closed 8000 NodeCache instances
> Tue Nov 18 15:59:45 GMT+00:00 2014 Started and Closed 9000 NodeCache instances
> Tue Nov 18 15:59:49 GMT+00:00 2014 Started and Closed 10000 NodeCache
> instances
> Tue Nov 18 16:00:01 GMT+00:00 2014 Started and Closed 11000 NodeCache
> instances
> java.lang.OutOfMemoryError: Java heap space
> at java.io.BufferedWriter.<init>(BufferedWriter.java:105)
> at java.io.BufferedWriter.<init>(BufferedWriter.java:88)
> at java.io.PrintStream.<init>(PrintStream.java:112)
> at java.io.PrintStream.<init>(PrintStream.java:175)
> at org.apache.jute.CsvOutputArchive.<init>(CsvOutputArchive.java:57)
> at
> org.apache.zookeeper.proto.RequestHeader.toString(RequestHeader.java:62)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at org.apache.zookeeper.ClientCnxn$Packet.toString(ClientCnxn.java:308)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:815)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:355)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068)
> java.lang.OutOfMemoryError: Java heap space
> at java.io.BufferedWriter.<init>(BufferedWriter.java:105)
> at java.io.BufferedWriter.<init>(BufferedWriter.java:88)
> at java.io.PrintStream.<init>(PrintStream.java:112)
> at java.io.PrintStream.<init>(PrintStream.java:175)
> at org.apache.jute.CsvOutputArchive.<init>(CsvOutputArchive.java:57)
> at
> org.apache.zookeeper.proto.RequestHeader.toString(RequestHeader.java:62)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at org.apache.zookeeper.ClientCnxn$Packet.toString(ClientCnxn.java:308)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:815)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:355)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068)
> java.lang.OutOfMemoryError: Java heap space
> at java.io.BufferedWriter.<init>(BufferedWriter.java:105)
> at java.io.BufferedWriter.<init>(BufferedWriter.java:88)
> at java.io.PrintStream.<init>(PrintStream.java:112)
> at java.io.PrintStream.<init>(PrintStream.java:175)
> at org.apache.jute.CsvOutputArchive.<init>(CsvOutputArchive.java:57)
> at
> org.apache.zookeeper.proto.RequestHeader.toString(RequestHeader.java:62)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at org.apache.zookeeper.ClientCnxn$Packet.toString(ClientCnxn.java:308)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:815)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:355)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068)
> java.lang.OutOfMemoryError: Java heap space
> at java.io.BufferedWriter.<init>(BufferedWriter.java:105)
> at java.io.BufferedWriter.<init>(BufferedWriter.java:88)
> at java.io.PrintStream.<init>(PrintStream.java:112)
> at java.io.PrintStream.<init>(PrintStream.java:175)
> at org.apache.jute.CsvOutputArchive.<init>(CsvOutputArchive.java:57)
> at
> org.apache.zookeeper.proto.RequestHeader.toString(RequestHeader.java:62)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at org.apache.zookeeper.ClientCnxn$Packet.toString(ClientCnxn.java:308)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:815)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:355)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068)
> Exception: java.lang.OutOfMemoryError thrown from the
> UncaughtExceptionHandler in thread "main"
> {noformat}
> Additional Notes:
> * When I don't specify the G1 collector I still get OutOfMemoryErrors, only
> the cause is "GC overhead limit exceeded".
> {noformat}java.lang.OutOfMemoryError: GC overhead limit exceeded
> at java.io.BufferedWriter.<init>(BufferedWriter.java:105)
> at java.io.BufferedWriter.<init>(BufferedWriter.java:88)
> at java.io.PrintStream.<init>(PrintStream.java:112)
> at java.io.PrintStream.<init>(PrintStream.java:175)
> at org.apache.jute.CsvOutputArchive.<init>(CsvOutputArchive.java:57)
> at
> org.apache.zookeeper.proto.GetDataRequest.toString(GetDataRequest.java:62)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at org.apache.zookeeper.ClientCnxn$Packet.toString(ClientCnxn.java:310)
> at java.lang.String.valueOf(String.java:2854)
> at java.lang.StringBuilder.append(StringBuilder.java:128)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:815)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
> at
> org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:355)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1068){noformat}
> * This has been around for a while as I first noticed it with v1.3.3. I
> upgraded to v2.6.0 and re-ran the test, but as you can see this still appears
> to be an issue.
> * I ran this test on a x86_64 Ubuntu 10.043 system and observed the same
> behavior
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