nhibernate性能之二级缓存篇

<property name="hibernate.cache.provider_class">NHibernate.Caches.SysCache.SysCacheProvider, NHibernate.Caches.SysCache</property>
        <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

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="NhibernateSample1.User,NhibernateSample1" table="Users" lazy="false">
    <cache usage="read-write"/>
    <id name="Id" column="Id" unsaved-value="0">
      <generator class="native" />
    </id>
    <property name="Name" column="Name" type="string" length="64" not-null="true" unique="true"></property>
    <property name="Pwd"  column="Pwd"  type="string" length="64" not-null="true"></property>
    <many-to-one name="Role"  class="NhibernateSample1.Role,NhibernateSample1" column="RoleID"></many-to-one>
   </class>
</hibernate-mapping>

NHibernateHelper.cs

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using NHibernate;
using NHibernate.Cfg;


namespace WebApp
{
    public sealed class NHibernateHelper
    {
        private const string CurrentSessionKey = "nhibernate.current_session";
        private static readonly ISessionFactory sessionFactory;

        static NHibernateHelper()
        {
            string cfgPath = @"E:\my project\nhibernate study\simple4\NHibernateStudy1\NhibernateSample1\hibernate.cfg.xml";
            sessionFactory = new NHibernate.Cfg.Configuration().Configure(cfgPath).BuildSessionFactory();
        }

        public static ISession GetCurrentSession()
        {
            HttpContext context = HttpContext.Current;
            ISession currentSession = context.Items[CurrentSessionKey] as ISession;

            if (currentSession == null)
            {
                currentSession = sessionFactory.OpenSession();
                context.Items[CurrentSessionKey] = currentSession;
            }

            return currentSession;
        }

        public static void CloseSession()
        {
            HttpContext context = HttpContext.Current;
            ISession currentSession = context.Items[CurrentSessionKey] as ISession;

            if (currentSession == null)
            {
                // No current session
                return;
            }

            currentSession.Close();
            context.Items.Remove(CurrentSessionKey);
        }

        public static void CloseSessionFactory()
        {
            if (sessionFactory != null)
            {
                sessionFactory.Close();
            }
        }
    }

}

页面代码:

 System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();
            ISession session = NHibernateHelper.GetCurrentSession();
            ITransaction tra = session.BeginTransaction();
            session.Load(typeof(NhibernateSample1.User), 1);
            tra.Commit();           
            sw.Stop();
            Response.Write(sw.ElapsedTicks+"<br>");
            sw.Reset();
            sw.Start();
            session = NHibernateHelper.GetCurrentSession();
            tra = session.BeginTransaction();
            session.Load(typeof(NhibernateSample1.User), 1);
            tra.Commit();           
            sw.Stop();
            Response.Write(sw.ElapsedTicks + "<br>");
            sw.Reset();
            sw.Start();
            session = NHibernateHelper.GetCurrentSession();
            session.Close();
            sw.Stop();
            Response.Write(sw.ElapsedTicks + "<br>");

第一次运行，用SQL事件探查器，结果为

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

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。