背景：实现blog网站，每篇文章的点播数统计。

简单实现方法：文章每次被打开时update一下数据库。如：

Update blog set visitcount=visitcount+1 where blogid=’文章ID’.

当然了，对于一些小型网站，根本没有什么人访问，这种实现方案完全没有问题。但是对于访问量比较大的网站，这种实现方案，很容易造成数据库over掉。

而且在执行update的时候，大多数据库默认都是使用排它锁的，这条数据是被锁住的，别人无法使用。访问量大，被锁住的机率也就大了。

我的方案：

先把统计数据缓存起来，每N秒钟写一次数据库，这样就大大的减少了数据库的连接次数，以及数据被锁住的机率。

缓存实现方案：

定义两个hashtable（t1,t2）。一个读一个写（读：从client接收数据。写：数据写入数据库）。每隔N秒写一次数据库。写数据库的时候最好采用异步的方式进行，以防止线程长期占用hashtable(读).

DEMO：

统计代码：VisitStatistic.ashx

在Blog文章页面中加入标签<script src=” VisitStatistic.ashx”></script>

VisitStatistic.ashx

代码：

    public class VisitStatistic : IHttpHandler

    {

        public void ProcessRequest(HttpContext context)

        {

            context.Response.ContentType = "text/plain";

            Statistic();

            context.Response.Write("");

        }

        private static object threadLock = new object();

        private static Hashtable t1 = Hashtable.Synchronized(new Hashtable());

        private static Hashtable t2 = Hashtable.Synchronized(new Hashtable());

        private static Timer time = new Timer(WriteToDb, null, 10, 6000);

        private static string readtb = "t1";

        private static bool isworking = false;

        private void Statistic()

        {

            lock (threadLock)

            {

                Hashtable ht = WriteTb;

                if (ht.ContainsKey(BlogId))

                {

                    ht[BlogId] = (int)ht[BlogId] + 1;

                }

                else

                {

                    ht.Add(BlogId, 1);

                }

            }

        }

        private static void WriteToDb(object obj)

        {

            if(isworking) return;

            isworking = true;

            Hashtable tb = ReadTb;

            IDictionaryEnumerator enumerator = tb.GetEnumerator();

            List<BlogStatistic> items = new List<BlogStatistic >(tb.Count);

            while (enumerator.MoveNext())

            {

                BlogStatistic item = new BlogStatistic () {

                    VisitCount = (int)enumerator.Value,

                    BlogId = (int)enumerator.Key

                };

                items.Add(item);

            }

            tb.Clear();

            if (items.Count > 0)

            {

                ThreadPool.QueueUserWorkItem(AsynWriteToDb, items);

            }

            if (readtb == "t1") readtb = "t2";

            else readtb = "t1";

            isworking = false;

        }

        private static void AsynWriteToDb(object items)

        {

            try

            {

                BlogBusiness business = new BlogBusiness ();

                business.AddBlogStatistic((List<BlogStatistic>)items);

            }

            catch (Exception ex)

            {

                LogMessage msg = new LogMessage(){

                    Message = "统计数写入数据库异常"

                };

                LogHelper.Error(msg, ex);

            }

        }

        private int BlogId

        {

            get

            {

                string util = HttpContext.Current.Request["blogid"];

                if(string.IsNullOrEmpty(util)

                    ||!Regex.IsMatch(util,@"^"d+$"))

                {

                    HttpContext.Current.Response.End();

                }

                return int.Parse(util);

            }

        }

        private static Hashtable ReadTb

        {

            get

            {

                if (readtb == "t1")

                {

                    return t1;

                }

                else

                {

                    return t2;

                }

            }

        }

        private static Hashtable WriteTb

        {

            get

            {

                if (readtb == "t1")

                {

                    return t2;

                }

                else

                {

                    return t1;

                }

            }

        }

        public bool IsReusable

        {

            get

            {

                return false;

            }

        }

    }