[AMQ-4977] Memory leak in ConnectionStateTracker when browsing non-empty queues

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.6.0, 5.7.0, 5.8.0, 5.9.0
• Fix Version/s: 5.9.1, 5.10.0
• Assignee: Timothy A. Bish
• Reporter: Georgi Danov
• Created: 16/Jan/14 22:53
• Updated: 27/May/14 15:20
• Resolved: 17/Jan/14 17:31

Description

I think I found case that is not handled by the fix AMQ-3316. We see memory leaks connected to this bug and after good amount of headbanging I think the problem is in how two methods work together - processMessagePull and trackBack. The first one has this piece of code:

  // leave a single instance in the cache
            final String id = pull.getDestination() + "::" + pull.getConsumerId();
            messageCache.put(id.intern(), pull);

while the second one unconditionally increases the currentCacheSize - regardless if the previous method added or replaced entry in the cache.

The situation where entries will be replaced (and not added) and the currentCacheSize will grow very fast until it wraps around and becomes negative is the following:

• have some logic that frequently creates queue browser and iterates through all the entries
• have the queue most of the time with at least one message. The more messages in the queue the faster currentCacheSize grows.

The reason is that processMessagePull reuses the consumer and destination ID for each browsed message in the queue when org.apache.activemq.ActiveMQQueueBrowser#hasMoreElements is invoked. trackBack is ignorant of this and keeps adding to the size regardless that the cache size stays the same.

Here is log from reproducing the issue as a proof:

2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 10000, 5 elements, pending scans:10, memory: 8951KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 20000, 10 elements, pending scans:10, memory: 10845KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 30000, 15 elements, pending scans:10, memory: 12645KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 40000, 20 elements, pending scans:10, memory: 10363KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 50000, 25 elements, pending scans:10, memory: 12169KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 60000, 30 elements, pending scans:10, memory: 9852KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 70000, 35 elements, pending scans:10, memory: 11657KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 80000, 40 elements, pending scans:10, memory: 9401KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 90000, 45 elements, pending scans:10, memory: 11222KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 100000, 50 elements, pending scans:10, memory: 13047KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 110000, 55 elements, pending scans:10, memory: 10767KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 120000, 60 elements, pending scans:10, memory: 12567KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 130000, 65 elements, pending scans:10, memory: 10256KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 138800, 67 elements, pending scans:10, memory: 12085KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 146800, 67 elements, pending scans:10, memory: 9745KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 154800, 67 elements, pending scans:10, memory: 11566KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 162800, 67 elements, pending scans:10, memory: 9225KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 170800, 67 elements, pending scans:10, memory: 11013KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 178800, 67 elements, pending scans:10, memory: 12812KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 186800, 67 elements, pending scans:10, memory: 10522KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 194800, 67 elements, pending scans:10, memory: 12328KB
2014-01-16 23:05:14  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 202800, 67 elements, pending scans:10, memory: 9999KB
2014-01-16 23:05:15  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 210800, 67 elements, pending scans:10, memory: 11805KB
2014-01-16 23:05:15  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 218800, 67 elements, pending scans:10, memory: 9496KB
2014-01-16 23:05:15  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 226800, 67 elements, pending scans:10, memory: 11316KB
2014-01-16 23:05:15  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 234800, 67 elements, pending scans:10, memory: 13100KB
2014-01-16 23:05:15  WARN ActiveMqMemoryLeakTest - MaxCacheSize: 131072, currentCacheSize: 242800, 67 elements, pending scans:10, memory: 10754KB

One can see that the garbage collection works well (cache does not grow) but the currentCacheSize keeps increasing
Unfortunately I cannot easily extract the original code and provide it. Hope the explanation is clear enough.

Issue Links

• relates to: AMQ-3316 Memory leak in ConnectionStateTracker with MessagePull objects