DOS命令删除指定文件夹下所有内容

来源：http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp

This document provides information on typical command-line options and environment variables that can affect the performance characteristics of the Java HotSpot Virtual Machine. Unless otherwise noted, all information in this document pertains to both the Java HotSpot Client VM and the Java HotSpot Server VM.

JVM Options For GC

Available Collectors

The discussion to this point has been about the serial collector. The Java HotSpot VM includes three different collectors, each with different performance characteristics.

1. The serial collector uses a single thread to perform all garbage collection work, which makes it relatively efficient since there is no communication overhead between threads. It is best-suited to single processor machines, since it cannot take advantage of multiprocessor hardware, although it can be useful on multiprocessors for applications with small data sets (up to approximately 100MB). The serial collector is selected by default on certain hardware and operating system configurations, or can be explicitly enabled with the option -XX:+UseSerialGC.
2. The parallel collector (also known as the throughput collector) performs minor collections in parallel, which can significantly reduce garbage collection overhead. It is intended for applications with medium- to large-sized data sets that are run on multiprocessor or multi-threaded hardware. The parallel collector is selected by default on certain hardware and operating system configurations, or can be explicitly enabled with the option -XX:+UseParallelGC.
   • New: parallel compaction is a feature introduced in J2SE 5.0 update 6 and enhanced in Java SE 6 that allows the parallel collector to perform major collections in parallel. Without parallel compaction, major collections are performed using a single thread, which can significantly limit scalability. Parallel compaction is enabled by adding the option -XX:+UseParallelOldGC to the command line.
3. The concurrent collector performs most of its work concurrently (i.e., while the application is still running) to keep garbage collection pauses short. It is designed for applications with medium- to large-sized data sets for which response time is more important than overall throughput, since the techniques used to minimize pauses can reduce application performance. The concurrent collector is enabled with the option -XX:+UseConcMarkSweepGC. 

JVM的自动垃圾收集（Garbage Collection）使得开发人员无需关注垃圾收集的细节，不过，当内存问题成为系统瓶颈的时候，我们就需要了解一下JVM的垃圾收集机制了。

最近需要参与一些java程序debug和性能调整方面的工作，jconsole是jdk自带的工具，比较好用，以下文章前面大部分翻译自：http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html ，后面关于用户名/密码和使用ssl加密连接的部分是从其他地方搜集的资料并且进行了验证。

作者:田逸(sery@163.com) from:http://blog.formyz.org/?p=148 

俗话说:工欲善其事,必先利其器.要做好系统管理,使自己的工作更轻松更有效的话,一个好的监控工具是必不可少的了.在这里我向大家推荐一款我使用了4年多的、功能强大、可灵活定制的开源监控利器—nagios。 

一 软件环境

本地客户端   ：           JProfiler5.2.1破解版

远程服务器端：           JProfiler5.2.2的linux版本+Tomcat5.5.27的linux版本+JDK1.5.0_11的linux版本。