nhibernate性能之二级缓存篇

╰+哭是因爲堅強的太久メ 2021-11-10 04:38 234阅读 0赞

1.学习目标  
   通过进一步学习nhibernate，了解二级缓存在nhiernate中的工作机制以及使用方法  
2.开发环境和必要准备  
    开发环境为:windows 2003,Visual studio .Net 2005,Sql server 2005 developer edition  
  必要准备：学习前五篇nhibernate学习系列[Nhibernate学习之起步篇-1][Nhibernate_-1]  ,[Nhibernate学习起步之many-to-one篇][Nhibernate_many-to-one] ,[Nhibernate学习之many-to-many篇][Nhibernate_many-to-many] ,[nhibernate学习之三级联(Ternary Associations)篇][nhibernate_Ternary Associations] ，[Nhibernate学习之性能改善1][Nhibernate_1]  
3.学前分析  
   在买电脑的时候，我们经常会看CPU的配置，其中衡量CPU性能的一项指标为二级缓存-Level 2 Cache,二级缓存越大，CPU性能越高。这是为什么，大家知道CPU的处理速度非常快，比在内存(memory)中的操作快上很多倍，这样在系统运行的时候，势必会造成一定的瓶颈效应，在内存和CPU之间加上一块处理速度在内存和处理器之间的介质-高速缓存，可以起到平衡的作用，每次CPU都试图先从高速缓存中读取数据，如果没有的话，再去内存中读取，一般CPU对高速缓存的命中率都在90%以上，所以大大提高了性能。在内存和磁盘之间加上一个高速缓存也可提高系统的新性能，减少对磁盘的IO次数  
4.如何在nhibernate中启动二级缓存  
   在nhiernate中的ISession对象中，已经存在了一级缓存，但是在ISession级别的，我们从上一节可以看出，ISession对象应该是尽早释放的，那依赖它的一级缓存会在它销毁的地时候销毁，所以一级缓存命中率比较低。而ISessionFactory对象推荐为不频繁创建，非常适用于Cache的使用，那这里的二级缓存正是ISessionFactory级别的。  
  要想在nhibernate中启用二级缓存，请在hibernate.cfg.xml中添加如下代码:

![None.gif][] < property  name ="hibernate.cache.provider\_class" > NHibernate.Caches.SysCache.SysCacheProvider, NHibernate.Caches.SysCache </ property >   
![None.gif][]         < property  name ="expiration" > 120 </ property >

NHibernate.Caches.SysCache.SysCacheProvider, NHibernate.Caches.SysCache还可以替换为NHibernate.Caches.`Prevalence``.PrevalenceCacheProvider, NHibernate.Caches.Prevalence,代表缓存的实现类，在bin目录中有这样两个dll`NHibernate.Caches.SysCache.dll,NHibernate.Caches.Prevalence.dll用哪个就把哪个拷贝到应用程序的bin目录下   
 expiration代表缓存过期时间，单位S  
设置完后，还需要在对象的映射文件中配置二级缓存的策略，比如我在User.hbm.xml中如下配置

![None.gif][] <? xml version="1.0" encoding="utf-8"  ?>   
![None.gif][] < hibernate-mapping  xmlns ="urn:nhibernate-mapping-2.2" >   
![None.gif][]   < class  name ="NhibernateSample1.User,NhibernateSample1"  table ="Users"  lazy ="false" >   
![None.gif][]     < cache  usage ="read-write" />   
![None.gif][]     < id  name ="Id"  column ="Id"  unsaved-value ="0" >   
![None.gif][]       < generator  class ="native"   />   
![None.gif][]     </ id >   
![None.gif][]     < property  name ="Name"  column ="Name"  type ="string"  length ="64"  not-null ="true"  unique ="true" ></ property >   
![None.gif][]     < property  name ="Pwd"   column ="Pwd"   type ="string"  length ="64"  not-null ="true" ></ property >   
![None.gif][]     < many-to-one  name ="Role"   class ="NhibernateSample1.Role,NhibernateSample1"  column ="RoleID" ></ many-to-one >   
![None.gif][]    </ class >   
![None.gif][] </ hibernate-mapping >

NHibernateHelper.cs

![None.gif][] using  System;  
![None.gif][] using  System.Data;  
![None.gif][] using  System.Configuration;  
![None.gif][] using  System.Web;  
![None.gif][] using  System.Web.Security;  
![None.gif][] using  System.Web.UI;  
![None.gif][] using  System.Web.UI.WebControls;  
![None.gif][] using  System.Web.UI.WebControls.WebParts;  
![None.gif][] using  System.Web.UI.HtmlControls;  
![None.gif][] using  NHibernate;  
![None.gif][] using  NHibernate.Cfg;  
![None.gif][]  
![None.gif][]  
![None.gif][] namespace  WebApp  
![ExpandedBlockStart.gif][]![ContractedBlock.gif][] ![dot.gif][] \{  
![InBlock.gif][]    public sealed class NHibernateHelper  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ![dot.gif][]\{  
![InBlock.gif][]        private const string CurrentSessionKey = "nhibernate.current\_session";  
![InBlock.gif][]        private static readonly ISessionFactory sessionFactory;  
![InBlock.gif][]  
![InBlock.gif][]        static NHibernateHelper()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]        ![dot.gif][]\{  
![InBlock.gif][]            string cfgPath = @"E:\\my project\\nhibernate study\\simple4\\NHibernateStudy1\\NhibernateSample1\\hibernate.cfg.xml";  
![InBlock.gif][]            sessionFactory = new NHibernate.Cfg.Configuration().Configure(cfgPath).BuildSessionFactory();  
![ExpandedSubBlockEnd.gif][]        \}  
![InBlock.gif][]  
![InBlock.gif][]        public static ISession GetCurrentSession()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]        ![dot.gif][]\{  
![InBlock.gif][]            HttpContext context = HttpContext.Current;  
![InBlock.gif][]            ISession currentSession = context.Items\[CurrentSessionKey\] as ISession;  
![InBlock.gif][]  
![InBlock.gif][]            if (currentSession == null)  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]            ![dot.gif][]\{  
![InBlock.gif][]                currentSession = sessionFactory.OpenSession();  
![InBlock.gif][]                context.Items\[CurrentSessionKey\] = currentSession;  
![ExpandedSubBlockEnd.gif][]            \}  
![InBlock.gif][]  
![InBlock.gif][]            return currentSession;  
![ExpandedSubBlockEnd.gif][]        \}  
![InBlock.gif][]  
![InBlock.gif][]        public static void CloseSession()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]        ![dot.gif][]\{  
![InBlock.gif][]            HttpContext context = HttpContext.Current;  
![InBlock.gif][]            ISession currentSession = context.Items\[CurrentSessionKey\] as ISession;  
![InBlock.gif][]  
![InBlock.gif][]            if (currentSession == null)  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]            ![dot.gif][]\{  
![InBlock.gif][]                // No current session  
![InBlock.gif][]                return;  
![ExpandedSubBlockEnd.gif][]            \}  
![InBlock.gif][]  
![InBlock.gif][]            currentSession.Close();  
![InBlock.gif][]            context.Items.Remove(CurrentSessionKey);  
![ExpandedSubBlockEnd.gif][]        \}  
![InBlock.gif][]  
![InBlock.gif][]        public static void CloseSessionFactory()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]        ![dot.gif][]\{  
![InBlock.gif][]            if (sessionFactory != null)  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]            ![dot.gif][]\{  
![InBlock.gif][]                sessionFactory.Close();  
![ExpandedSubBlockEnd.gif][]            \}  
![ExpandedSubBlockEnd.gif][]        \}  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]\}   
![None.gif][]

页面代码:

![None.gif][]  System.Diagnostics.Stopwatch sw  =   new  System.Diagnostics.Stopwatch();  
![None.gif][]            sw.Start();  
![None.gif][]            ISession session  =  NHibernateHelper.GetCurrentSession();  
![None.gif][]            ITransaction tra  =  session.BeginTransaction();  
![None.gif][]            session.Load( typeof (NhibernateSample1.User),  1 );  
![None.gif][]            tra.Commit();             
![None.gif][]            sw.Stop();  
![None.gif][]            Response.Write(sw.ElapsedTicks \+ " <br> " );  
![None.gif][]            sw.Reset();  
![None.gif][]            sw.Start();  
![None.gif][]            session  =  NHibernateHelper.GetCurrentSession();  
![None.gif][]            tra  =  session.BeginTransaction();  
![None.gif][]            session.Load( typeof (NhibernateSample1.User),  1 );  
![None.gif][]            tra.Commit();             
![None.gif][]            sw.Stop();  
![None.gif][]            Response.Write(sw.ElapsedTicks  \+   " <br> " );  
![None.gif][]            sw.Reset();  
![None.gif][]            sw.Start();  
![None.gif][]            session  =  NHibernateHelper.GetCurrentSession();  
![None.gif][]            session.Close();  
![None.gif][]            sw.Stop();  
![None.gif][]            Response.Write(sw.ElapsedTicks  \+   " <br> " );

第一次运行，用SQL事件探查器，结果为  
![ssds343df.JPG][]  
从截图中的SQL语句看，第一次从数据库中加在User数据  
第二次  
![23f434.JPG][]  
从图中可以看出，第二次加载User对象,并没有从数据中获取数据，而是将没有设置Cache的Role信息从User里面获取。  
当然在利用缓存的时候，缓存不会知道另外一个进程存储的实体发生变化，应该自己建立一些策略来及时地更新缓存快照。而且当ISessionFactory销毁的时候，二级缓存也会随之销毁，这也是应用的时候，应该注意的。今天先写到这，有点困了。

转载于:https://www.cnblogs.com/jillzhang/archive/2007/04/02/697489.html

[Nhibernate_-1]: http://www.cnblogs.com/jillzhang/archive/2007/03/21/683067.html
[Nhibernate_many-to-one]: http://www.cnblogs.com/jillzhang/archive/2007/03/23/684567.html
[Nhibernate_many-to-many]: http://www.cnblogs.com/jillzhang/archive/2007/03/23/685750.html
[nhibernate_Ternary Associations]: http://www.cnblogs.com/jillzhang/archive/2007/04/01/695583.html
[Nhibernate_1]: http://www.cnblogs.com/jillzhang/archive/2007/04/01/686079.html
[None.gif]: /images/20211109/e2442196eedb4f46af5569a86659afad.png
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[InBlock.gif]: /images/20211109/3f1cab1351ab4a2288ffc7bfbb1668bf.png
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[23f434.JPG]: /images/20211109/15c296c624824679a7afae03a7c0bbd5.png