Java Used Heap RAM usage peaks, how can I avoid them?

Question

First of all, I can't really show code, I am sorry, these software belongs to the company I work for, not me. I will try to explain my problem the best I can.

I am developing a little application based on JavaFX, that shows values in LineCharts, these are refreshed every 800ms-1000ms (0,8-1 seconds), and calls System.gc() every time I refresh (Around once every 0,8-1 seconds).

I am having RAM usage peaks every 10-20 seconds:

In this specific example, this doesn't look like a problem, but in some cases it goes up to 700-750 MB (Making the Heap Size go up to 1.2-1.3 GB, and taking a long time to release it back to the OS).

I know about (and currently use, without noticing any huge improvement) Heap Tuning Paremeters, but I don't think these can fix the problem here, they are helping at specific points, and slightly reduce the memory consumption, but not solve the problem.

Any ideas on how can I design my code not to have these RAM peaks? I don't have a process that uses memory and releases it every 10-20 seconds, so I assume there is something else allocating and releasing that ammount of RAM (Maybe JavaFX?), JVisualVM only says int[], byte[] and char[], and I am not even using Integer values in my code (I work with Double values in this software).

Thank you all.

Answer 1

I found the solution:

Both MrSmith42 and GhostCat pointed out that calling System.gc() doesn't really help me here. They were right, in fact, that was the problem.

Removing System.gc() solved the problem for me

Thank you, MrSmith42 and GhostCat.

Answer 2

System.gc() does not trigger a garbage collection directly it is more like a hint to the VM that you think performing a garbage collection would be a good idea. What your VM does is its own decision based on the implementation. Only if the VM runs out of memory it will sure perform a garbage collection but that also without you calling System.gc(). A quite long discussion about this topic can be found here:

When does System.gc() do anything

Answer 3

Sorry, but the only reasonable answer here: you have to do profiling in order to understand where those peaks are coming from. You have to identify the root cause of this problem; and that is nothing that we can help with.

This program runs in your setup, with your data, and shows behavior that needs to analyzed over time.

My guess would be that your program is creating large amounts of objects that will be thrown away quickly afterwards ( I guess you have those calls to System.gc() in there for a reason). And guess what: creating garbage on high rate is a bad idea. Because it keeps your GC constantly spinning; and it (obviously?!) contributes to high memory load.

So, as said: you have to identify the root cause and fix that. In that sense: you have to study the tooling you are using. An alternative to profiling might be to have the GC log its activities; and analyze that output. See here for some information on that.