CODEWITHSUNDEEP
javatomcatmemory-leaksjvmheap-memory
user1826116
user1826116

Reputation: 415

Increasing heap memory utilization on Java Tomcat application

I have a Java application running on a Tomcat7 instance. I am using Java 8.

Now within my application there is a webservice of the format : http://zzz.xxx.zzz.xxx/someWebservice?somepar1=rrr&somePar2=yyy. This returns a String value of max 10 characters.

I have now started load testing this service using Jmeter. I am putting a load of 100 concurrent connections and getting a throughput of roughly 150 requests/second. The server is a 4 core-6GB machine and is only running Tomcat (application instance). The database instance is running on a separate machine. JVM is running with min 2GB and Max 4 GB memory allocation. Max Perm Size is 512 MB. Tomcat has enough threads to cater to my load (Max connections/threads/executor values have been setup correctly)

I am now trying to optimize this service and in order to do so I am trying to analyze memory consumption. I am using JConsole for the same. My CPU usage is not a concern , but when I look at the memory (HEAP) usage, I feel something is not right. What I observe is a sawtooth shaped graph, which I know is correct as regular GC clears heap memory.

My concern is that this sawtooth shaped graph has an upward trend. I mean that the troughs in the sawtooth seem to be increasing over time. With this trend eventually my server reaches max heap memory in an hour or so and then stabilizes at 4GB. I believed that if I am putting a CONSTANT load, then the heap memory utilization should have a constant trend, i.e. a saw tooth graph with its peaks and troughs aligned. If there is an upward trend I am suspecting that there is a memory leak of variables which are collecting over time and since GC isn't able to clear them there is an increase over a period of time. I am attaching a screenshot.

Heap Usage

Questions:

1). Is this normal behavior? If yes, then why does the heap continuously increase despite no change in load? I don't believe that a load of 100 threads should saturate 4GB heap in roughly 30 minutes.

2). What could be the potential reasons here? Do I need to look at memory leaks? Any JVM analyzer apart from JConsole which can help me pinpoint the variables which the GC is unable to clear?

Upvotes: 0

Views: 792

Answers (1)

the8472
the8472

Reputation: 43125

The see-saw pattern most likely stems from minor-collections, the dip around 14:30 then is a major collection, which you did not take into account when doing your reasoning.

Your load may simply be so low that it needs a long time to reach a stable state.

With this trend eventually my server reaches max heap memory in an hour or so and then stabilizes at 4GB.

Supports that conclusion if you're not seeing any OOMEs.

But there's only so much one can deduce from such charts. If you want to know more you should enable GC logging and inspect the log outputs instead.

Upvotes: 3

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