CS中缓存对性能的优化起了非常大的作用，今天做一次深入的研究。经过大致的代码浏览发现CS中的缓存分为2种：一种采用System.Web.Caching，另一种采用HttpContext.Items（由于CS大量的采用服务器端控件没有使用页面级的缓存）。
首先研究一下System.web.Caching.Cache的使用
在CommunityServerComponents项目中发现了CommunityServer.Components.CSCache，查看一下代码
private CSCache(){} //>> Based on Factor = 5 default value public static readonly int DayFactor = 17280; public static readonly int HourFactor = 720; public static readonly int MinuteFactor = 12; private static readonly Cache _cache; private static int Factor = 5; public static void ReSetFactor(int cacheFactor) { Factor = cacheFactor; } /// /// Static initializer should ensure we only have to look up the current cache /// instance once. /// static CSCache() { HttpContext context = HttpContext.Current; if(context != null) { _cache = context.Cache; } else { _cache = HttpRuntime.Cache; } }
发现其实是对System.Web.Caching.Cache作了一个封装（在CS中这样的例子比比皆是如：CSContext），主要实现了一下功能：
1、插入：Insert、MicroInsert（插入生存周期短的缓存项目）、Max（插入生存周期很长的缓存项目，在系统运行期间永久缓存）
2、获取：Get
3、移除：Remove、RemoveByPattern
4、全部清除：Clear
另外大家看一下“private static int Factor = 5;”，如果希望不用缓存则直接设置为Factor=0即可，如果希望延长缓存生存周期则适当调大Factor值，也可以在CommunityServer.config中修改“cacheFactor”的数值。
在解决方案中搜索一下“CSCache”，会发现有63个文件，分析一下缓存内容主要有2种类型：配置文件及从数据库读取的实体。
一个是配置文件信息（例如：CommunityServer.Configuration.CSConfiguration、CommunityServer.Galleries.Components.GalleryConfiguration、CommunityServer.Blogs.Components.WeblogConfiguration等）
例如CommunityServer.Configuration.CSConfiguration
public static CSConfiguration GetConfig() { CSConfiguration config = CSCache.Get(CacheKey) as CSConfiguration; if(config == null) { string path; if(HttpContext.Current != null) path = HttpContext.Current.Server.MapPath("~/communityserver.config"); else path = Directory.GetCurrentDirectory() + Path.DirectorySeparatorChar + "communityserver.config"; XmlDocument doc = new XmlDocument(); doc.Load(path); config = new CSConfiguration(doc); CSCache.Max(CacheKey,config,new CacheDependency(path)); CSCache.ReSetFactor(config.CacheFactor); } return config; }
可以看到对communityserver.config的配置信息在第一次使用时从配置文件中读取出来并加入采用CSCache.Max()永久缓存，其失效策略为communityserver.config文件的更改。回顾一下，System.Web.Caching.Cache的失效策略一般有三种情况：文件的更改、缓存中其他缓存内容的更改、定义失效时间。GalleryConfiguration及WeblogConfiguration内的缓存失效策略是第2种情况的一个示例
public static WeblogConfiguration Instance() { string cacheKey = "WeblogConfiguration"; WeblogConfiguration config = CSCache.Get(cacheKey) as WeblogConfiguration; if(config == null) { XmlNode node = CSConfiguration.GetConfig().GetConfigSection("CommunityServer/Weblog"); config = new WeblogConfiguration(); ... CacheDependency dep = new CacheDependency(null, new string[]{CSConfiguration.CacheKey}); CSCache.Insert(cacheKey, config, dep); } return config; }
另一种是数据库实体的缓存，以CommunityServer.Discussions.Components.Posts为例
public static PostSet GetPosts(int postID, int pageIndex, int pageSize, int sortBy, int sortOrder) { PostSet postSet; CSContext csContext = CSContext.Current; string key = "Forum-Posts::P:{0}-PI:{1}-PS:{2}-SB:{3}-SO:{4}"; string postCollectionKey = string.Format(key,postID,pageIndex,pageSize, sortBy, sortOrder); // Attempt to retrieve from Cache postSet = CSCache.Get(postCollectionKey) as PostSet; // forumContext.Context.Cache[postCollectionKey]; if (postSet == null) { // Create Instance of the CommonDataProvider ForumDataProvider dp = ForumDataProvider.Instance(); postSet = dp.GetPosts(postID, pageIndex, pageSize, sortBy, sortOrder, CSContext.Current.User.UserID, true); CSCache.Insert(postCollectionKey,postSet,6); } return postSet; }
GetPosts()首先从缓存中读取postSet = CSCache.Get(postCollectionKey) as PostSet;
如果缓存中不存在则从数据库中读取并放入缓存（缓存失效策略为定义的时间段），这是CS减少数据库连接次数最有效的方式。另外其缓存key值的设置规则也是非常值得学习的。
然后研究一下HttpContext.Items的使用
HttpContext.Items被Rob Howard称之为“每请求缓存”（参见编写高性能 Web 应用程序的 10 个技巧），故名思义即缓存只存在于HttpRequest请求期间，请求结束后缓存即失效。
CS中采用CSContext对HttpContext作了封装，搜索一下“CSContext.Items”发现有7个文件。以CommunityServer.Discussions.Components.Forums为例，分析一下代码
private static Hashtable GetForums(CSContext csContext, bool ignorePermissions, bool cacheable, bool flush) { Hashtable unfilteredForums = null; Hashtable forums; int settingsID = CSContext.Current.SiteSettings.SettingsID; string cacheKey = string.Format("Forums-Site:{0}",settingsID); string localKey = string.Format("ForumsForUser:{0}",ignorePermissions); if(flush) { CSCache.Remove(cacheKey); csContext.Items[localKey] = null; } #if DEBUG_NOCACHE cacheable = false; #endif // Have we already fetched for this request? // //If something is in the context with the current cache key, we have already processed and validated this request! unfilteredForums = csContext.Items[localKey] as Hashtable; //We do not need to revalidate this collection on the same request if((unfilteredForums != null)) return unfilteredForums; else if(!cacheable) csContext.Items.Remove(cacheKey); //Is it safe to use the cached version? if ((!cacheable)) CSCache.Remove(cacheKey); //If we find the forums in the cache, we need to revalidate them. DO NOT return the coolection unless //the call specifies ignorepermissions unfilteredForums = CSCache.Get(cacheKey) as Hashtable; // Get the raw forum groups // if ( unfilteredForums == null ) { unfilteredForums = ForumDataProvider.Instance().GetForums(); // Dynamically add the special forum for private messages // unfilteredForums.Add( 0, PrivateForum() ); // Cache if we can // if (cacheable) CSCache.Insert(cacheKey,unfilteredForums,CSCache.MinuteFactor * 15,CacheItemPriority.High); } // Are we ignoring permissions? // if (ignorePermissions) { //Save us the logic look up later csContext[localKey] = unfilteredForums; return unfilteredForums; } // We need to create a new hashtable // forums = new Hashtable(); User user = CSContext.Current.User; // Filter the list of forums to only show forums this user // is allowed to see // foreach (Forum f in unfilteredForums.Values) { // The forum is added if the user can View, Read // if( Permissions.ValidatePermissions(f,Permission.View,user) ) if(f.IsActive || user.IsForumAdministrator) forums.Add(f.SectionID, f); } // Insert into request cache // csContext[localKey] = forums; return forums; }
第一次访问时首先从数据库中读取数据并存储到Cache及HttpContext.Items中，但是请求结束后HttpContext.Items的缓存即可消失，到底能起什么作用呢？搜索GetForums()发现有多个服务器端控件使用这个方法，如果有多个其中的控件出现在一个页面即一个请求中时，则缓存就发生作用了。
