#设置虚拟机IO权重
virsh blkiotune
--weight IO Weight
--device-weights per-device IO Weights, in the form of /path/to/device,weight,...
--device-read-iops-sec per-device read I/O limit per second, in the form of /path/to/device,read_iops_sec,...
--device-write-iops-sec per-device write I/O limit per second, in the form of /path/to/device,write_iops_sec,...
--device-read-bytes-sec per-device bytes read per second, in the form of /path/to/device,read_bytes_sec,...
--device-write-bytes-sec per-device bytes wrote per second, in the form of /path/to/device,write_bytes_sec,...
--config affect next boot
--live affect running domain
--current affect current domain
#virsh blkiotune Centos6 --weight 500 --live
#设置虚拟机磁盘具体IO
virsh blkdeviotune
--total-bytes-sec total throughput limit, as scaled integer (default bytes)
--read-bytes-sec read throughput limit, as scaled integer (default bytes)
--write-bytes-sec write throughput limit, as scaled integer (default bytes)
--total-iops-sec total I/O operations limit per second
--read-iops-sec read I/O operations limit per second
--write-iops-sec write I/O operations limit per second
--total-bytes-sec-max total max, as scaled integer (default bytes)
--read-bytes-sec-max read max, as scaled integer (default bytes)
--write-bytes-sec-max write max, as scaled integer (default bytes)
--total-iops-sec-max total I/O operations max
--read-iops-sec-max read I/O operations max
--write-iops-sec-max write I/O operations max
--size-iops-sec I/O size in bytes
--group-name group name to share I/O quota between multiple drives
--total-bytes-sec-max-length duration in seconds to allow total max bytes
--read-bytes-sec-max-length duration in seconds to allow read max bytes
--write-bytes-sec-max-length duration in seconds to allow write max bytes
--total-iops-sec-max-length duration in seconds to allow total I/O operations max
--read-iops-sec-max-length duration in seconds to allow read I/O operations max
--write-iops-sec-max-length duration in seconds to allow write I/O operations max
--config affect next boot
--live affect running domain
--current affect current domain
#virsh blkdeviotune Centos6 vda --total-bytes-sec 10240
I/O from the guest is not cached on the host, but may be kept in a writeback disk cache. Use this option for guests with large I/O requirements.（guest 使用 writeback， host 不使用 page cache，相当于 guest 直接访问主机磁盘。） 这种模式下虚拟机磁盘镜像文件或者块设备会使用 O_DIRECT 语义， 则 host 的 page cache 被绕过， I/O 直接在 qemu-kvm 的用户空间 buffers 和 host 的存储设备间发生。因为实际存储设备可能在写数据放到写队列后就上报写完成，虚拟机上的存储控制器被告知有回写缓存（writeback cache）， 所以 guest 需要下发刷盘（flush）命令来保证数据一致（落盘）。相当于直接访问 host 磁盘，性能不错。 在虚拟机中使用此选项来满足大多数需求，是支持迁移的最佳和唯一选项。
writethrough
I/O from the guest is cached on the host but written through to the physical medium. This mode is slower and prone to scaling problems. Best used for small number of guests with lower I/O requirements. Suggested for guests that do not support a writeback cache (such as Red Hat Enterprise Linux 5.5 and earlier), where migration is not needed. 数据完整性得到保障（不经过写缓存，而是直接写到物理磁盘），读操作性能较好，写操作性能较差。
writeback
I/O from the guest is cached on the host. Both the host page cache and the disk write cache are enabled，读写操作性能都很优异，唯一的缺点就是写操作的数据掉电可能丢失，无法保证数据完整性。qemu-kvm1.2版本以上为默认缓存模式。
directsync
Similar to writethrough, but I/O from the guest bypasses the host page cache. 两种缓存均关闭，读写操作性能较差。
unsafe
The host may cache all disk I/O, and sync requests from guest are ignored. guest发出的刷新缓存指令被忽视，意味着以牺牲数据的完整性来换取性能的提升。
default
If no cache mode is specified, the system's default settings are chosen.
缓存选项
IO模式
Linux系统上异步IO常见的有两种实现，一种是kernel native AIO，另外一种是threaded aio: user space AIO emulated by posix thread workers。 Kernel native AIO : Kernel的原生态异步IO实现。 Threaded AIO : Linux用户空间异步IO的实现，其实它不是真正的异步IO，是通过启动一定数量的blocking IO线程来模拟异步IO。这种实现有不少缺点，毕竟有不少线程开销，还在改进中。默认是Thread模式
#设置虚拟机内存配额
memtune
OPTIONS
[--domain] domain name, id or uuid
#虚机可用最大内存
--hard-limit Max memory, as scaled integer (default KiB)
#发生内存争用时，内存的限制
--soft-limit Memory during contention, as scaled integer (default KiB)
#虚拟机加上swap的最大内存
--swap-hard-limit Max memory plus swap, as scaled integer (default KiB)
#虚拟机保证分配的最小内存
--min-guarantee Min guaranteed memory, as scaled integer (default KiB)
--config affect next boot
--live affect running domain
--current affect current domain
spring JMS对于异步消息处理基本上只需配置下就能进行高效的处理。其核心就是消息侦听器容器，常用的类就是DefaultMessageListenerContainer。该容器可配置侦听器的并发数量，以及配合MessageListenerAdapter使用消息驱动POJO进行消息处理。且消息驱动POJO是放入TaskExecutor中进行处理，进一步提高性能，减少侦听器的阻塞。具体配置如下：
ZIP文件的解压缩实质上就是从输入流中读取数据。Java.util.zip包提供了类ZipInputStream来读取ZIP文件,下面的代码段创建了一个输入流来读取ZIP格式的文件;
ZipInputStream in = new ZipInputStream(new FileInputStream(zipFileName));
&n
Spring可以通过注解@Transactional来为业务逻辑层的方法(调用DAO完成持久化动作)添加事务能力，如下是@Transactional注解的定义：
/*
* Copyright 2002-2010 the original author or authors.
*
* Licensed under the Apache License, Version
使用nginx lua已经两三个月了，项目接开发完毕了，这几天准备上线并且跟高德地图对接。回顾下来lua在项目中占得必中还是比较大的，跟PHP的占比差不多持平了，因此在开发中遇到一些问题备忘一下 1：content_by_lua中代码容量有限制，一般不要写太多代码，正常编写代码一般在100行左右（具体容量没有细心测哈哈，在4kb左右），如果超出了则重启nginx的时候会报 too long pa
import java.util.Stack;
public class ReverseStackRecursive {
/**
* Q 66.颠倒栈。
* 题目：用递归颠倒一个栈。例如输入栈{1,2,3,4,5}，1在栈顶。
* 颠倒之后的栈为{5,4,3,2,1}，5处在栈顶。
*1. Pop the top element
*2. Revers
仅作笔记使用
public class VectorQueue {
private final Vector<VectorItem> queue;
private class VectorItem {
private final Object item;
private final int quantity;
public VectorI
