[jira] Issue Comment Edited: (AXIS2-4749) Tribe's AtMostOnceInterceptor could lead to OutOfMemory under heavy load and big messages.

["Afkham Azeez (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AXIS2-4749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881270#action_12881270 ] 

Afkham Azeez edited comment on AXIS2-4749 at 6/22/10 2:02 PM:
--------------------------------------------------------------

Stefano,
Two different messages can have the same hashcode. So, if you simply store the hashcode & compare them, some distinct messages will be detected as duplicates, and will lead to message processing losses. 

There is a cleanup task which cleans up this Map, so this Map will not grow infinitely. Also, you could turn off at-most-once message processing if you do not require it using a configuration parameter in the axis2.xml file. 

      was (Author: afkham_azeez):
    Stefano,
Two different messages can have the same hashcode. So, if you simply store the hashcode & compare them, some distinct messages will be detected as duplicates, and will lead to message processing losses. 

There is a cleanup task which cleans up this Map, so this Map will not grow infinitely. Also, you could turn off at-most-once message processing if you do not require it using an configuration parameter in the axis2.xml file. 
  
> Tribe's AtMostOnceInterceptor could lead to OutOfMemory under heavy load and big messages.
> ------------------------------------------------------------------------------------------
>
>                 Key: AXIS2-4749
>                 URL: https://issues.apache.org/jira/browse/AXIS2-4749
>             Project: Axis2
>          Issue Type: Bug
>    Affects Versions: 1.6
>         Environment: Linux 64 bit, JDK 1.6, WSO2 Carbon 2.0.3
>            Reporter: Stefano Bruna
>
> Wa are stressing the WSO2 ESB with some cache mediator enabled. Messages are echanged by tribes through the cluster's nodes. Under heavy load and with some big xml messages (1 mb per message) the local variable Map<ChannelMessage, Long> receivedMessages is growing continuously leading to a potential Out of Memory if the cleaning thread that runs every 5 minutes is not fast enough to free up memory.
> See: http://svn.apache.org/viewvc/axis/axis2/java/core/trunk/modules/clustering/src/org/apache/axis2/clustering/tribes/AtMostOnceInterceptor.java?view=markup
> This is because when an object is passed to a HashMap as a key internally the original object is kept. The Hasmap is using a private class Entry that has the hash, the orginal object used to create the hash, and the value that, in this usage case, is a long.
> Somewhere inside HashMap.java
>         // private variables
> 	  final Object key;
>         Object value;
>         Entry next;
>         final int hash;
> 	  // constructor 
>         Entry(int i, Object obj, Object obj1, Entry entry)
>         {
>             value = obj1; <==== value, ok
>             next = entry; <===== entry with the same hash
>             key = obj; <======= orginal object, needed for the equals use in case of same hash
>             hash = i; <======== key, ok 
>         }
> So if the AtMostOnceInterceptor manages for example 50 msg/sec and a message is 1 mb we could have within 5 minutes a memory usage for the messageReceived object of 6 GB.
> A simple solution, if we dont'to accept all this as something by desing, could be to pass to the HashMap the already calculated hash of the object (that is also the same method that is called internally  int i = hash(obj.hashCode());) to not give the opportunity to the HashMap to keep the actual object used to produce the key.
> .....
> // map
>  private static final Map<Integer, Long> receivedMessagesHashCodes =
>             new HashMap<Integer, Long>();
> .....
> Integer hashCode = new Integer(msg.hashCode());
>             	
> if (receivedMessagesHashCodes.get(hashCode) == null) {  // If it is a new message, keep track of it
>         receivedMessagesHashCodes.put(hashCode, System.currentTimeMillis());
>         super.messageReceived(msg);
> } else {  // If it is a duplicate message, discard it. i.e. dont call super.messageReceived
>         log.info("Duplicate message received from " + TribesUtil.getName(msg.getAddress()));
> }
> etc...
> but maybe is not strong enough in the case tow messages have the same hash. A FIFO queue with a limited capacity  ?

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