#MINECRAFT MEMORY CLEANER HOW TO#
#MINECRAFT MEMORY CLEANER CODE#

In particular, an application that does I/O with large multi-megabyte buffers at startup but does I/O with small buffers may see a benefit to using this property. Applications with certain patterns of I/O usage may benefit from using this property. If the property is not set, then no limit is put on the size of buffers that are cached. The value of the property is the maximum capacity of a direct buffer that can be cached. 'The system property has been introduced in 8u102 to limit the memory used by the 'temporary buffer cache.' The temporary buffer cache is a per-thread cache of direct memory used by the NIO implementation to support applications that do I/O with buffers backed by arrays in the Java heap. The Oracle documentation explains the above property as follows:Ībility to limit the capacity of buffers that can be held in the temporary buffer cache:

In JDK version 1.8u102 or newer, use JVM property to limit the per-thread DirectByteBuffer size. Reduce the number of I/O threads, if possible

#MINECRAFT MEMORY CLEANER CODE#

When this issue occurs in the code that you cannot change, like a third-party library, the only ways to address this problem are: Here is what the DirectByteBuffer cache maintained by a group of threads running identical I/O code looks like in the JXRay report: To diagnose this problem, you can take and analyze the JVM heap dump using the JXRay memory analysis tool ( Despite the fact that the memory in question is allocated outside the heap, the heap dump has enough information: each DirectByteBuffer has the capacity data field that specifies the amount of native memory reserved by this buffer. This blog post explains the problem in more details and provides an example that reproduces it and links to the relevant (old) JDK source code for those who are really interested. Native memory regions used by the given thread are released only when the thread terminates, and subsequently, the GC reaches that thread’s DirectByteBuffer instance(s). As a result, if a Java app creates many threads that perform I/O using HeapByteBuffers, and/or these buffers are big, the JVM process may end up using a lot of additional native memory that looks like a leak. Thus, if your code (or some I/O library, such as Netty) uses a HeapByteBuffer for I/O, its contents are always copied to or from a temporary DirectByteBuffer that's created by the JDK under the hood.įurthermore, the JDK caches one or more DirectByteBuffers per thread, and by default, there is no limit on the number or size of these buffers. Each buffer kind has its pros and cons, but what’s important is that the OS can read and write bytes only from or to native memory. They are created by ByteBuffer.allocate() and ByteBuffer.allocateDirect() calls, respectively. is an abstract class its concrete subclasses are HeapByteBuffer, which simply wraps a byte array and the DirectByteBuffer that allocates off-heap memory. The Java NIO APIs use ByteBuffers to read and write data. If you have little time, you can go straight to the checklist in section 5, and then read only the most relevant part(s) of this article. Other than that, in rare situations, native memory might be over-consumed by JVM internals, such as class metadata, or the OS may essentially give an app more memory than it needs.īelow, we will discuss all these situations in greater detail. This memory is released when this class’ equivalent of “finalize” Java method is called - either automatically, when the DirectByteBuffer instance is GCed, or manually, which is rare. When such an object is created, it makes an internal call that allocates the amount of native memory equal to the buffer capacity. In pure Java applications, the most common native memory consumers are instances of. However, it turns out that even pure Java apps can sometimes use a significant amount of off-heap memory, and when it happens, it's not easy to understand what's going on.

#MINECRAFT MEMORY CLEANER HOW TO#

We assume that, if you write native code, you already know how to debug it. In this article, we will not cover 'mixed' applications that contain both Java and native code. If this is not something that you anticipated, and you want to understand what's going on, do you know where to start? If not, read on. However, in some situations, you may discover that your app's RSS (total memory used by the process) is much bigger than its heap size. For most apps, this amount is relatively modest.

Almost every Java application uses some native (off-heap) memory.

Minecraft memory cleaner