易栈网-膘叔

在看云风的BLOG的时候，他说游戏处理中IO的开销非常大，甚至一些IO会堵塞1~2秒。细想在WEB应用中，IO的开销就好象没有它那么高了，但一些应用了框架的系统还是会有很高的IO开销。
最早的时候，我是和同事们在考虑，是否系统在起动的时候，就把项目COPY到内存里，然后指定WEB目录为内存中的目录，当然涉及到写操作还是用管道引用到外面。这样的话，程序的IO就可以完全忽略掉了，只是，这个涉及到了，启动顺序和其他一些操作，还得写上不少的shell等，后来就完全搁浅了。这是在linux平台下。
后来，自己有了服务器，用的win平台。于是这时候我也尝试用ramdisk开辟了128M左右的空间用来做WEB应用。我当时的一些Cache的操作也是放在这128M空间里的。只是效果嘛，看不出，因为是自己的小应用，没有访问量。。。。但至少这是可行的（设置ramdisk的时候是关机时保存到磁盘，这样下次开机的时候它还会存在而不会被删除）
云风在博客中说他们用了RDB的结构来处理，即从B（backup）引到一部分数据到R（Ram）里面，然后写的时候，先写到R，然后用脚本増量到D（data）中，这样保证了B只读，D只写，内存R读写一起上。减少了大量的运行时IO开销。
该博客有很多评论，比如有建议用nosql的，有建议其他方法的，比如有个人就介绍了这个flashcache，看看觉得有意思就复制了下来。。。
关于flashcache的原文，在这里：http://www.orczhou.com/index.php/2010/09/flachcache-first-view/。。。

Flashcache是Facebook技术团队的又一力作，最初是为加速MySQL设计的。Flashcache是在Linux层面的，所以任何受磁盘IO困绕的软件或应用都可以方便的使用之。

1. Why Flashcache

随着时间的流逝，网站上的数据一直在不停的积累。如果你经营的只是一个博客的话，这不会是问题，因为10G的空间，大概就够你写一辈子了（如果放在硬盘上，其实一辈子很短）。如果你恰巧在一个快速增长的公司，数据会越来越多，从MB，到GB，再到TB。

如果将这些数据全部放在大容量的SATA、SAS盘上时，会发现性能（响应时间）不够；如果全放在SSD上时，又会发现成本很高。即使公司能够大气 到都放到SSD上，你会发现1TB的数据里面可能只有200G是经常被访问的，300G可能偶尔被访问到，最后剩下的500G可能已经成为历史数据了，几 乎不被访问到，如果全部都放在SSD上有略有浪费。于是就有了Flashcache。

Flashcache一个非常不错的软件（准确的说是一个Linux的模块）， 可以动态加载。Flashcache通过在文件系统（VFS）和设备驱动之间新增了一次缓存层，来实现对热门的缓存。Flashcache是另一种缓存， 一般用SSD作为介质的缓存（一般的缓存用的是内存），通过将传统硬盘上的热门数据缓存到SSD上，然后利用SSD优秀的读性能，来加速系统。这个方法较 之内存缓存，没有内存快，但是空间可以比内存大很多。

本文是一个关于Flashcache的初步介绍。

2. 谁适合用Flashcache

数据量很大（例如4TB），热门数据也很大（800GB），不必要或者不舍得全部买内存来缓存。

3. 谁不适合用Flashcache

数据量不大的话，一般Flashcache就没什么用武之地了，内存就可以帮你解决问题了；

不差钱，买内存呗；

另外Flashcache的加入也使得系统的复杂度增加了一层，如果你坚持KISS原则（Keep it simple, Stupid!），也可以弃用之。

4. 基本原理图

上图中，Flashcache将普通的SAS盘（/dev/sda）和一个高速的SSD(/dev/sdb)虚拟成一个带缓存的块设备（/dev/mapper/cachedev）。后续还将会有更多关于Flashcache相关的文章出现，敬请期待。

5. Flashcache是否只是一个过渡产品

对于当前，PCI接口的SSD价格还十分昂贵，而随着时间的推移，价格会降；另外，根据摩尔定律，未来会有更快的设备出现，所以Flashcache是一个“持久的”产品，还只是一个过渡软件，这并不好说。

关注未来新技术的发展吧:)

参考：

1. Facebook / Flashcache

2. Releasing Flashcache of Facebook

3. flashcache-doc.txt

PS：写完整篇文章，最大的收获是：发现人的一生其实很短、很短，可能连1GB都不到。

1、DBANOTES中介绍QUORA的一句话：“Quora 大量使用 Amazon EC2 与 S3 服务；操作系统部署的是 Ubuntu Linux，易于部署和管理；静态内容用 Cloudfront.服务分发，图片先传到 EC2 服务器，使用 Pyhon S3 API 处理后后传到 S3。”【Quora 用了哪些技术 ?】。

我想说的是，UbuntuServer看来也越来越被N多人所接受了。原来的那种以centos等为主流的观念也开始慢慢的向ubuntu上转移了，虽然只是很少的一部分，但任何事物都要有个过程的嘛 。

2、来自“为之漫笔”的《NetBeans之父Jaroslav Tulach谈软件框架设计》，其中有一些话确实会引起人的共鸣：

• “API的第一个版本绝对不会完美”
• “不可能知道使用你的库的所有人”

API第一个版本绝对不会完美，这个其实是所有写代码的人遇到的最常见的问题，问题总是在不断的开发中被发现的，如果你是在不停的修正BUG，那框架还能继续下去，如果发现问题就重写，那框架永远也完成不了。。。。

3、张鑫旭的博客上有些CSS和JQuery的插件不错。比如这个：jQuery powerFloat万能浮动层下拉层插件。地址在：http://www.zhangxinxu.com/wordpress/?p=1328，还有一个弹出窗框架也挺好。一些简单的应用完全足够了。。

dd

三八节看起来不象是我们男性过的节日，但事实上，在三八节，我真的要感谢很多人。。。
远的就不说了，以前那些老师啥的很多都是女性的。

就从身边吧，感谢我的母亲，感谢我的岳母，感谢我的妻子。这三个人是我最想表达感谢之意的。

母亲生我养我，这是毋庸置疑的，当然得感谢。

岳母和岳父每天辛苦的帮我们照顾小朋友，我父母又不在上海，岳父母承担的压力就大了，几乎是天天在照顾着小孩（几乎每个小孩都是自己爷爷奶奶或者外公外婆带大的吧。），我和妻子回家又晚，她们辛苦极了。

最后感谢我的妻子，除了因为爱情，还有小朋友啊。虽然我更喜欢小姑娘多一点，但小家伙也是个很可爱的人呢。

这是一篇来自Yii官方的文章，写在了1.1.6的new fetures里面，值得一看，最起码，你在看完后，下次被人面试的时候，问到什么 是MVC，你可以有回答的东西了。

不多说，上原文，内容也不复杂，所以我就不翻译了（其实是我翻译不来，将就着看看可以，可是要翻译成人人都能看得懂的内容就难了）。。。

原文来自于：http://www.yiiframework.com/doc/guide/1.1/en/basics.best-practices，目前官方也确实没有中文版。

Although Model-View-Controller (MVC) is known by nearly every Web developer, how to properly use MVC in real application development still eludes many people. The central idea behind MVC is code reusability and separation of concerns. In this section, we describe some general guidelines on how to better follow MVC when developing a Yii application.

To better explain these guidelines, we assume a Web application consists of several sub-applications, such as

• front end: a public-facing website for normal end users;
• back end: a website that exposes administrative functionality for managing the application. This is usually restricted to administrative staff;
• console: an application consisting of console commands to be run in a terminal window or as scheduled jobs to support the whole application;
• Web API: providing interfaces to third parties for integrating with the application.

The sub-applications may be implemented in terms of modules, or as a Yii application that shares some code with other sub-applications.

1. Model 

Models represent the underlying data structure of a Web application. Models are often shared among different sub-applications of a Web application. For example, a LoginForm model may be used by both the front end and the back end of an application; a News model may be used by the console commands, Web APIs, and the front/back end of an application. Therefore, models

• should contain properties to represent specific data;

• should contain business logic (e.g. validation rules) to ensure the represented data fulfills the design requirement;

• may contain code for manipulating data. For example, a SearchForm model, besides representing the search input data, may contain a search method to implement the actual search.

Sometimes, following the last rule above may make a model very fat, containing too much code in a single class. It may also make the model hard to maintain if the code it contains serves different purposes. For example, a News model may contain a method named getLatestNews which is only used by the front end; it may also contain a method named getDeletedNews which is only used by the back end. This may be fine for an application of small to medium size. For large applications, the following strategy may be used to make models more maintainable:

• Define a NewsBase model class which only contains code shared by different sub-applications (e.g. front end, back end);

• In each sub-application, define a News model by extending from NewsBase. Place all of the code that is specific to the sub-application in this News model.

So, if we were to employ this strategy in our above example, we would add a News model in the front end application that contains only the getLatestNews method, and we would add another News model in the back end application, which contains only the getDeletedNews method.

In general, models should not contain logic that deals directly with end users. More specifically, models

• should not use $_GET, $_POST, or other similar variables that are directly tied to the end-user request. Remember that a model may be used by a totally different sub-application (e.g. unit test, Web API) that may not use these variables to represent user requests. These variables pertaining to the user request should be handled by the Controller.

• should avoid embedding HTML or other presentational code. Because presentational code varies according to end user requirements (e.g. front end and back end may show the detail of a news in completely different formats), it is better taken care of by views.

2. View 

Views are responsible for presenting models in the format that end users desire. In general, views

• should mainly contain presentational code, such as HTML, and simple PHP code to traverse, format and render data;

• should avoid containing code that performs explicit DB queries. Such code is better placed in models.

• should avoid direct access to $_GET, $_POST, or other similar variables that represent the end user request. This is the controller's job. The view should be focused on the display and layout of the data provided to it by the controller and/or model, but not attempting to access request variables or the database directly.

• may access properties and methods of controllers and models directly. However, this should be done only for the purpose of presentation.

Views can be reused in different ways:

• Layout: common presentational areas (e.g. page header, footer) can be put in a layout view.

• Partial views: use partial views (views that are not decorated by layouts) to reuse fragments of presentational code. For example, we use _form.php partial view to render the model input form that is used in both model creation and updating pages.

• Widgets: if a lot of logic is needed to present a partial view, the partial view can be turned into a widget whose class file is the best place to contain this logic. For widgets that generate a lot of HTML markup, it is best to use view files specific to the widget to contain the markup.

• Helper classes: in views we often need some code snippets to do tiny tasks such as formatting data or generating HTML tags. Rather than placing this code directly into the view files, a better approach is to place all of these code snippets in a view helper class. Then, just use the helper class in your view files. Yii provides an example of this approach. Yii has a powerful CHtml helper class that can produce commonly used HTML code. Helper classes may be put in an autoloadable directory so that they can be used without explicit class inclusion.

3. Controller 

Controllers are the glue that binds models, views and other components together into a runnable application. Controllers are responsible for dealing directly with end user requests. Therefore, controllers

• may access $_GET, $_POST and other PHP variables that represent user requests;

• may create model instances and manage their life cycles. For example, in a typical model update action, the controller may first create the model instance; then populate the model with the user input from $_POST; after saving the model successfully, the controller may redirect the user browser to the model detail page. Note that the actual implementation of saving a model should be located in the model instead of the controller.

• should avoid containing embedded SQL statements, which are better kept in models.

• should avoid containing any HTML or any other presentational markup. This is better kept in views.

In a well-designed MVC application, controllers are often very thin, containing probably only a few dozen lines of code; while models are very fat, containing most of the code responsible for representing and manipulating the data. This is because the data structure and business logic represented by models is typically very specific to the particular application, and needs to be heavily customized to meet the specific application requirements; while controller logic often follows a similar pattern across applications and therefore may well be simplified by the underlying framework or the base classes.