应用DirectBuffer提升系统性能

Java 2 SE 6 doc :

Given a direct byte buffer, the Java virtual machine will make a best effort to perform native I/O operations directly upon it. That is, it will attempt to avoid copying the buffer’s content to (or from) an intermediate buffer before (or after) each invocation of one of the underlying operating system’s native I/O operations.

• DirectBuffer通过免去中间交换的内存拷贝, 提升IO处理速度;

Java 2 SE 6 doc :

The contents of direct buffers may reside outside of the normal garbage-collected heap, and so their impact upon the memory footprint of an application might not be obvious.

• DirectBuffer在-XX:MaxDirectMemorySize=xxM大小限制下^[1], 使用Heap之外的内存, GC对此”无能为力”^[2] ,也就意味着规避了在高负载下频繁的GC过程对应用线程的中断影响.

因此, 当系统应用场景满足:

• 大量原生类型数据使用
• 频繁IO操作
• 系统处理响应速度要求快且稳定

典型场景是网络数据传输, 可考虑合理应用DirectBuffer.

1. MappedByteBuffer不受-XX:MaxDirectMemorySize=xxM大小限制.
2. DirectBuffer何时被回收, 可参见http://www.simaliu.com/archives/274.html.

Tags: gc, io, java