[转载]简单利用Memcached进行缓存层设计

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[转载]简单利用Memcached进行缓存层设计 – Jeff Wong – 博客园.

正在考虑web应用缓存层的设计,参考了不少资料,估计还是需要用到相对成熟应用广泛的分布式缓存Memcached。在.net平台上早就有相对成熟的Memcached客户端产品,如BeITMemcachedEnyimMemcached,业余时间看了一下源码,自己分析并调用一下并不困难。这里简单介绍一下利用Memcached的一个简单的缓存层设计,示例代码基于EnyimMemcached,下面以贴代码为主。

一、公共缓存接口

分析ASP.NET web caching的缓存类,我们大致可以抽象出如下几个接口方法:

namespace DotNet.Common.EnyimCache
{
///
/// memcached公共缓存调用方法接口(读)
///
public interface ICacheReaderService
{

///
/// 返回指定key的对象
///
///
<span> </span> ///
object Get(string key);

///
/// 返回指定key的对象
///
///
///
<span> </span> ///
T Get(string key);

///
/// 是否存在
///
///
<span> </span> ///
bool isExists(string key);
}

///
/// memcached公共缓存调用方法接口(写)
///
public interface ICacheWriterService
{
///
/// 缓存有效间隔时间 (以分钟为单位)
///
int TimeOut { set; get; }

///
/// 添加指定key的对象
///
///
<span> </span> ///
<span> </span> void Add(string key, object obj);

///
/// 添加指定key的对象
///
///
///
<span> </span> ///
<span> </span> void Add(string key, T obj);

///
/// 移除指定key的对象
///
///
<span> </span> bool Remove(string key);

///
/// 修改指定key的对象
///
///
<span> </span> ///
bool Modify(string key, object destObj);

///
/// 清空缓存
///
///
bool Release();
}
}

看命名就知道,增删改查是也。根据个人使用缓存的经验,修改操作通常是不需要的,如果确实需要修改缓存数据,直接删除然后添加就是改了。

还有,你可能会问,这里为什么要定义两个接口?原因主要是考虑到读操作(查询)是经常使用的,而写操作(增删改)相对较少,所以也把它们设计成读写分离的方式。

二、缓存服务实现

这里就需要调用Memcached客户端封装好的调用方法,实现增删改查等方法。

using System;

namespace DotNet.Common.EnyimCache
{
using Enyim.Caching.Memcached;

public class CacheReaderService : BaseService, ICacheReaderService
{

public int TimeOut
{
get;
set;
}

public CacheReaderService()
{

}

public object Get(string key)
{
object obj = null;
Client.TryGet(key, out obj);
return obj;
}

public T Get(string key)
{
object obj = Get(key);
T result = default(T);
if (obj != null)
{
result = (T)obj;
}
return result;
}

public bool isExists(string key)
{
object obj = Get(key);
return (obj == null) ? false : true;
}
}

public class CacheWriterService : BaseService, ICacheWriterService
{
public int TimeOut
{
get;
set;
}

public CacheWriterService()
{

}

public CacheWriterService(int timeOut)
{
this.TimeOut = timeOut;
}

public void Add(string key, object obj)
{
if (TimeOut &gt; 0)
{
Client.Store(StoreMode.Add, key, obj, DateTime.Now.AddMinutes(TimeOut));
}
else
{
Client.Store(StoreMode.Add, key, obj);
}
}

public void Add(string key, T obj)
{
if (TimeOut &gt; 0)
{
Client.Store(StoreMode.Add, key, obj, DateTime.Now.AddMinutes(TimeOut));
}
else
{
Client.Store(StoreMode.Add, key, obj);
}
}

public bool Remove(string key)
{
return Client.Remove(key);
}

public bool Modify(string key, object destObj)
{
return Client.Store(StoreMode.Set, key, destObj);
}

///
/// 清空缓存 TO DO
///
///
public bool Release()
{
throw new NotImplementedException();
}
}
}

基类里初始化一个MemcachedClient示例Client,这个Client的方法里封装了较多的函数。查看源码可以知道,它们本质上都是 向Memcached服务端发送相关指令(run command),然后解析返回的二进制数据,如果您熟悉memcached所使用的协议,理解起来应该会相当简单。本文示例只使用了客户端提供的几个方 法。

同时要注意,在实现具体缓存服务的时候,CacheWriterService有两个构造函数,其中带参数的是为缓存显式指定过期时间。这个参数在实际应用中通常需要配置,显然是比较灵活一些的。

备注:在接口中有一个函数Release,本来的目标是清空所有的缓存数据,但是客户端没有直接提供对应的函数,如果您有好的方法,请不吝赐教。

三、简单的读写测试

贴一下字符串、时间、单个类和集合的增删改查示例代码:

ICacheWriterService writer = CacheBuilder.GetWriterService();//writer 使用memcached默认过期时间
ICacheReaderService reader = CacheBuilder.GetReaderService();//reader

#region 字符串

string strKey = "hello";

bool isOK = writer.Remove(strKey); //移除
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

writer.Add(strKey, "hello world"); //添加
Console.WriteLine("Add key {0}, value:hello world", strKey);

bool isExists = reader.isExists(strKey);//是否存在
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

string result = reader.Get(strKey) as string;//查询
Console.WriteLine("Get key {0}:{1}", strKey, result);

bool isModify = writer.Modify(strKey, "Hello Memcached!");//修改
Console.WriteLine("Modify key {0}, value:Hello Memcached. The result is:{1}", strKey, isModify);

result = reader.Get(strKey);
Console.WriteLine("Generic get key {0}:{1}", strKey, result);

isOK = writer.Remove(strKey);
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

isExists = reader.isExists(strKey);
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

result = reader.Get(strKey) as string;
Console.WriteLine("Get key {0}:{1}", strKey, result);

result = reader.Get(strKey);
Console.WriteLine("Generic get key {0}:{1}", strKey, result);
Console.WriteLine();
Console.WriteLine("===========================================");
Console.Read();

#endregion

#region 时间

DateTime dtNow = DateTime.Now;
strKey = "datetime";
isOK = writer.Remove(strKey); //移除
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

writer.Add(strKey, dtNow); //添加
Console.WriteLine("Add key {0}, value:{1}", strKey, dtNow);

isExists = reader.isExists(strKey);//是否存在
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

DateTime dt = (DateTime)reader.Get(strKey);//查询
Console.WriteLine("Get key {0}:{1}", strKey, dt);

dt = reader.Get(strKey);
Console.WriteLine("Generic get key {0}:{1}", strKey, dt);

isOK = writer.Remove(strKey);
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

isExists = reader.isExists(strKey);
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

Console.WriteLine("Get key {0}:{1}", strKey, reader.Get(strKey));

Console.WriteLine("Generic get key {0}:{1}", strKey, reader.Get(strKey));//default(datetime)
Console.WriteLine();
Console.WriteLine("===========================================");

Console.Read();

#endregion

#region 类

dtNow = DateTime.Now;
Province province = new Province(13579, "江苏", dtNow, dtNow);

strKey = string.Format("{0}_{1}", province.GetType().Name, province.Id);//省
isOK = writer.Remove(strKey); //移除
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

writer.Add(strKey, province); //添加
Console.WriteLine("Add key {0}, value:{1}", strKey, dtNow);

isExists = reader.isExists(strKey);//是否存在
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

Province queryProvince = (Province)reader.Get(strKey);//查询
Console.WriteLine("Get key {0}:{1}", strKey, queryProvince.ProvinceName);

queryProvince = reader.Get
(strKey);
Console.WriteLine("Generic get key {0}:{1}", strKey, queryProvince.ProvinceName);

isOK = writer.Remove(strKey);
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

isExists = reader.isExists(strKey);
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

Console.WriteLine("Get key {0}:{1}", strKey, reader.Get(strKey));

Console.WriteLine("Generic get key {0}:{1}", strKey, reader.Get
(strKey));
Console.WriteLine();
Console.WriteLine("===========================================");

Console.Read();

#endregion

#region 集合(列表)

dtNow = DateTime.Now;
IList listCities = new List();
City city = new City(135, province.Id, "南京", "210000", dtNow, dtNow);
listCities.Add(city);
city = new City(246, province.Id, "苏州", "215000", dtNow, dtNow);
listCities.Add(city);

strKey = string.Format("List_{0}_{1}_{2}", province.GetType().Name, province.Id, city.GetType().Name);//省份对应城市
isOK = writer.Remove(strKey); //移除
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

writer.Add(strKey, listCities); //添加
Console.WriteLine("Add key {0}, value:", strKey);
foreach (var item in listCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Id, item.CityName);
}

isExists = reader.isExists(strKey);//是否存在
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

IList queryCities = reader.Get(strKey) as IList;//查询
Console.WriteLine("Get key {0}:", strKey);
foreach (var item in queryCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Id, item.CityName);
}

queryCities = reader.Get&gt;(strKey);
Console.WriteLine("Generic get key {0}:", strKey);
foreach (var item in queryCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Id, item.CityName);
}

isOK = writer.Remove(strKey);
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

isExists = reader.isExists(strKey);
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

Console.WriteLine("Get key {0}:{1}", strKey, reader.Get(strKey));

Console.WriteLine("Generic get key {0}:{1}", strKey, reader.Get&gt;(strKey));
Console.WriteLine();
Console.WriteLine("===========================================");

Console.Read();

#endregion

#region 集合(字典)

dtNow = DateTime.Now;
IDictionary dictCities = new Dictionary();
city = new City(123, province.Id, "镇江", "212000", dtNow, dtNow);
dictCities.Add(city.Id, city);
city = new City(321, province.Id, "扬州", "225000", dtNow, dtNow);
dictCities.Add(city.Id, city);

strKey = string.Format("Dictionary_{0}_{1}_{2}", province.GetType().Name, province.Id, city.GetType().Name);//省份对应城市
isOK = writer.Remove(strKey); //移除
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

writer.Add(strKey, dictCities); //添加
Console.WriteLine("Add key {0}, value:", strKey);
foreach (var item in dictCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Key, item.Value.CityName);
}

isExists = reader.isExists(strKey);//是否存在
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

IDictionary queryDictCities = reader.Get(strKey) as IDictionary;//查询
Console.WriteLine("Get key {0}:", strKey);
foreach (var item in queryDictCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Key, item.Value.CityName);
}

queryDictCities = reader.Get&gt;(strKey);
Console.WriteLine("Generic get key {0}:", strKey);
foreach (var item in queryDictCities)
{
Console.WriteLine("CityId:{0} CityName:{1}", item.Key, item.Value.CityName);
}

isOK = writer.Remove(strKey);
Console.WriteLine("Removed key {0}:{1}", strKey, isOK);

isExists = reader.isExists(strKey);
Console.WriteLine("Key {0} exists:{1}", strKey, isExists);

Console.WriteLine("Get key {0}:{1}", strKey, reader.Get(strKey));

Console.WriteLine("Generic get key {0}:{1}", strKey, reader.Get&gt;(strKey));
Console.WriteLine();
Console.WriteLine("===========================================");

Console.Read();

#endregion

这里就不贴全部代码了,文章最后有示例可以下载。

在我的简单测试中,对常见基础数据类型如(字符串、数组、数字和时间)、集合(列表和字典)都有良好的表现,对datatable和dataset同样表现不俗,但是不太建议直接缓存这两种重粒度的类型。

在显式指定过期时间的示例中,指定过期时间是一分钟,但是memcached实际过期时间有时候好像会多于一分钟,估计是系统内部的延迟。

在本地计算机上进行10万次循环添加缓存的过程中,发现系统内存果然增加的非常厉害。然后查询性能并没有显著下降,也许和我的单机测试环境有关,所以我认为测试结果并没有说服力,要知道,memcached的优势是它的分布式缓存实现。

有人发现如何保证缓存系统的键唯一也非常令人头疼。同样的缓存框架,不同项目不同开发者如何保证自己程序添加的缓存键唯一呢?有一种简单方法就是通 过拼接字符串成为有意义的主键,比如按照项目名、命名空间、类名、数据库中的主键组合构成主键等等。当然了,在查询的时候也要自己封装特定格式的字符串主 键。个人感觉确实是一个行之有效的方法。

demo下载:SimpleCacheApp

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