Java: JVM memory consumption

Question

I am playing around with Java, parameter -Xms and class Runtime.

I see that JVM allocates about 15% of the memory that is available - regardless how much it is.

Runtime rt Runtime.getRuntime ();
long total = rt.totalMemory ()
long free = rt.freeMemory ();

That is the case if I start my programm with paramter

-Xms4000m

as well as with

-Xms90m

I see the difference of Xms in the result of totalMemory.

I understand the strategy of allocating more from the beginning to avoid expensive reallocation.

But I do not know if that is in place here AND how I can meter the real memory-consumption of my program.

gc logging is the easiest way

Erik
– Erik

2018-09-20 08:57:48 +00:00
Commented Sep 20, 2018 at 8:57 — Erik
– Erik, Commented Sep 20, 2018 at 8:57
Did you mean to specify -Xmx instead?

Mark Rotteveel
– Mark Rotteveel

2018-09-20 09:03:02 +00:00
Commented Sep 20, 2018 at 9:03 — Mark Rotteveel
– Mark Rotteveel, Commented Sep 20, 2018 at 9:03
no, Xms is the parameter that affects totalMemory

chris01
– chris01

2018-09-20 09:06:25 +00:00
Commented Sep 20, 2018 at 9:06 — chris01
– chris01, Commented Sep 20, 2018 at 9:06

Markus · Accepted Answer · 2018-09-20 09:01:33Z

1

If your're using the Oracle JVM, you can use the command line tool jmap or the GUI tool jvisualvm to measure the heap consumption of your Java program.

answered Sep 20, 2018 at 9:01

Markus

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Sugan · Accepted Answer · 2018-09-20 09:03:58Z

1

Get the PID of the application and you can use top command in the below way to print out the statistics.

top -b | grep PID

You can see how the memory is utilized over time.

answered Sep 20, 2018 at 9:03

Sugan

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