CODEWITHSUNDEEP
javamemorygarbage-collectionbenchmarking
Dmitry
Dmitry

Reputation: 4442

java heap size grows by portions up to some limit

I am writing a simple server application in Java, and I'm making some benchmarks using Apache benchmark now.

Right after the start the resident memory used by server is about 40M. I make the series of 1000 requests (100 concurrent requests). After each series I check the memory usage again. The result seems very strange to me.

During the first runs of benchmark, the 99% of requests are processed in ≈20 msecs and the rest 1% of them in about 300 msecs (!). Meantime the memory usage grows. After 5-7 runs this growth stops at 120M and requests begin to run much faster - about 10 msecs per request. Moreover, thee time and mem values remain the same when I increase the number of requests.

Why could this happen? If there was a memory leak then my server would require more and more resources. I could only suggest that this is because of some adaptive JVM memory allocation mechanism which increases the heap size in advance.

Upvotes: 0

Views: 580

Answers (1)

Boris the Spider
Boris the Spider

Reputation: 61148

The heap starts out at Xms and grows as needed up to the specified limit Xmx.

It is normal for the JVM to take a while to "warn up" - all sorts of optimisations happen at run time.

If the memory climbs up to a point and then stops climbing, you are fine.

If the memory climbs indefinitely and the program eventually throws an OutOfMemoryError then you have a problem.

From your description it looks as if the former is true, so no memory leak.

Upvotes: 2

Related Questions