Ed *_*mes 9 c# asp.net caching
在C#ASP.net应用程序中缓存数据时,有没有人建议哪种方法更好？
我目前正在使用两种方法的组合,一些数据(列表,字典,通常的特定于域的信息)直接放入缓存并在需要时装箱,一些数据保存在globaldata类中,并通过该方法检索class(即GlobalData类被缓存,它的属性是实际数据).
这两种方法都更好吗？
我觉得从并发的角度来看,单独缓存每个项目会更加明智,但是从长远来看,它创建了更多的工作,其中更多的功能完全处理从Utility类中的缓存位置获取数据.
建议将不胜感激.
通常,缓存的性能比底层源(例如DB)好得多,因此缓存的性能不是问题.主要目标是获得尽可能高的缓存命中率(除非您正在大规模开发,因为这样才能获得优化缓存的成果).
为了实现这一点,我通常会尽可能让开发人员尽可能直接使用缓存(这样我们就不会因为开发人员懒得使用缓存而错过任何缓存命中的机会).在某些项目中,我们使用Microsoft企业库中提供的CacheHandler的修改版本.
使用CacheHandler(使用策略注入),您可以通过向其添加属性轻松地使方法"可缓存".例如:
[CacheHandler(0, 30, 0)]
public Object GetData(Object input)
{
}
会使对该方法的所有调用都缓存30分钟.所有调用都根据输入数据和方法名称获取一个唯一的缓存键,因此如果您使用不同的输入调用该方法两次,它将不会被缓存,但如果您在输出相同的时间间隔内调用它> 1次,则方法只执行一次.
我们的修改版本如下所示:
using System;
using System.Diagnostics;
using System.IO;
using System.Reflection;
using System.Runtime.Remoting.Contexts;
using System.Text;
using System.Web;
using System.Web.Caching;
using System.Web.UI;
using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;
using Microsoft.Practices.Unity.InterceptionExtension;
namespace Middleware.Cache
{
/// <summary>
/// An <see cref="ICallHandler"/> that implements caching of the return values of
/// methods. This handler stores the return value in the ASP.NET cache or the Items object of the current request.
/// </summary>
[ConfigurationElementType(typeof (CacheHandler)), Synchronization]
public class CacheHandler : ICallHandler
{
/// <summary>
/// The default expiration time for the cached entries: 5 minutes
/// </summary>
public static readonly TimeSpan DefaultExpirationTime = new TimeSpan(0, 5, 0);
private readonly object cachedData;
private readonly DefaultCacheKeyGenerator keyGenerator;
private readonly bool storeOnlyForThisRequest = true;
private TimeSpan expirationTime;
private GetNextHandlerDelegate getNext;
private IMethodInvocation input;
public CacheHandler(TimeSpan expirationTime, bool storeOnlyForThisRequest)
{
keyGenerator = new DefaultCacheKeyGenerator();
this.expirationTime = expirationTime;
this.storeOnlyForThisRequest = storeOnlyForThisRequest;
}
/// <summary>
/// This constructor is used when we wrap cached data in a CacheHandler so that
/// we can reload the object after it has been removed from the cache.
/// </summary>
/// <param name="expirationTime"></param>
/// <param name="storeOnlyForThisRequest"></param>
/// <param name="input"></param>
/// <param name="getNext"></param>
/// <param name="cachedData"></param>
public CacheHandler(TimeSpan expirationTime, bool storeOnlyForThisRequest,
IMethodInvocation input, GetNextHandlerDelegate getNext,
object cachedData)
: this(expirationTime, storeOnlyForThisRequest)
{
this.input = input;
this.getNext = getNext;
this.cachedData = cachedData;
}
/// <summary>
/// Gets or sets the expiration time for cache data.
/// </summary>
/// <value>The expiration time.</value>
public TimeSpan ExpirationTime
{
get { return expirationTime; }
set { expirationTime = value; }
}
#region ICallHandler Members
/// <summary>
/// Implements the caching behavior of this handler.
/// </summary>
/// <param name="input"><see cref="IMethodInvocation"/> object describing the current call.</param>
/// <param name="getNext">delegate used to get the next handler in the current pipeline.</param>
/// <returns>Return value from target method, or cached result if previous inputs have been seen.</returns>
public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)
{
lock (input.MethodBase)
{
this.input = input;
this.getNext = getNext;
return loadUsingCache();
}
}
public int Order
{
get { return 0; }
set { }
}
#endregion
private IMethodReturn loadUsingCache()
{
//We need to synchronize calls to the CacheHandler on method level
//to prevent duplicate calls to methods that could be cached.
lock (input.MethodBase)
{
if (TargetMethodReturnsVoid(input) || HttpContext.Current == null)
{
return getNext()(input, getNext);
}
var inputs = new object[input.Inputs.Count];
for (int i = 0; i < inputs.Length; ++i)
{
inputs[i] = input.Inputs[i];
}
string cacheKey = keyGenerator.CreateCacheKey(input.MethodBase, inputs);
object cachedResult = getCachedResult(cacheKey);
if (cachedResult == null)
{
var stopWatch = Stopwatch.StartNew();
var realReturn = getNext()(input, getNext);
stopWatch.Stop();
if (realReturn.Exception == null && realReturn.ReturnValue != null)
{
AddToCache(cacheKey, realReturn.ReturnValue);
}
return realReturn;
}
var cachedReturn = input.CreateMethodReturn(cachedResult, input.Arguments);
return cachedReturn;
}
}
private object getCachedResult(string cacheKey)
{
//When the method uses input that is not serializable
//we cannot create a cache key and can therefore not
//cache the data.
if (cacheKey == null)
{
return null;
}
object cachedValue = !storeOnlyForThisRequest ? HttpRuntime.Cache.Get(cacheKey) : HttpContext.Current.Items[cacheKey];
var cachedValueCast = cachedValue as CacheHandler;
if (cachedValueCast != null)
{
//This is an object that is reloaded when it is being removed.
//It is therefore wrapped in a CacheHandler-object and we must
//unwrap it before returning it.
return cachedValueCast.cachedData;
}
return cachedValue;
}
private static bool TargetMethodReturnsVoid(IMethodInvocation input)
{
var targetMethod = input.MethodBase as MethodInfo;
return targetMethod != null && targetMethod.ReturnType == typeof (void);
}
private void AddToCache(string key, object valueToCache)
{
if (key == null)
{
//When the method uses input that is not serializable
//we cannot create a cache key and can therefore not
//cache the data.
return;
}
if (!storeOnlyForThisRequest)
{
HttpRuntime.Cache.Insert(
key,
valueToCache,
null,
System.Web.Caching.Cache.NoAbsoluteExpiration,
expirationTime,
CacheItemPriority.Normal, null);
}
else
{
HttpContext.Current.Items[key] = valueToCache;
}
}
}
/// <summary>
/// This interface describes classes that can be used to generate cache key strings
/// for the <see cref="CacheHandler"/>.
/// </summary>
public interface ICacheKeyGenerator
{
/// <summary>
/// Creates a cache key for the given method and set of input arguments.
/// </summary>
/// <param name="method">Method being called.</param>
/// <param name="inputs">Input arguments.</param>
/// <returns>A (hopefully) unique string to be used as a cache key.</returns>
string CreateCacheKey(MethodBase method, object[] inputs);
}
/// <summary>
/// The default <see cref="ICacheKeyGenerator"/> used by the <see cref="CacheHandler"/>.
/// </summary>
public class DefaultCacheKeyGenerator : ICacheKeyGenerator
{
private readonly LosFormatter serializer = new LosFormatter(false, "");
#region ICacheKeyGenerator Members
/// <summary>
/// Create a cache key for the given method and set of input arguments.
/// </summary>
/// <param name="method">Method being called.</param>
/// <param name="inputs">Input arguments.</param>
/// <returns>A (hopefully) unique string to be used as a cache key.</returns>
public string CreateCacheKey(MethodBase method, params object[] inputs)
{
try
{
var sb = new StringBuilder();
if (method.DeclaringType != null)
{
sb.Append(method.DeclaringType.FullName);
}
sb.Append(':');
sb.Append(method.Name);
TextWriter writer = new StringWriter(sb);
if (inputs != null)
{
foreach (var input in inputs)
{
sb.Append(':');
if (input != null)
{
//Diffrerent instances of DateTime which represents the same value
//sometimes serialize differently due to some internal variables which are different.
//We therefore serialize it using Ticks instead. instead.
var inputDateTime = input as DateTime?;
if (inputDateTime.HasValue)
{
sb.Append(inputDateTime.Value.Ticks);
}
else
{
//Serialize the input and write it to the key StringBuilder.
serializer.Serialize(writer, input);
}
}
}
}
return sb.ToString();
}
catch
{
//Something went wrong when generating the key (probably an input-value was not serializble.
//Return a null key.
return null;
}
}
#endregion
}
}
微软最值得赞扬的是这段代码.我们只在请求级别添加缓存等内容而不是跨请求(比您想象的更有用)并修复了一些错误(例如,将DateTime-objects序列化为不同的值).
Ed，我假设这些列表和字典包含几乎静态的数据，过期的可能性很小。然后，有些数据会被频繁点击，但更改也更频繁，因此您可以使用 HttpRuntime 缓存来缓存它。
现在，您应该考虑所有数据以及不同类型之间的所有依赖关系。如果您从逻辑上发现 HttpRuntime 缓存的数据在某种程度上取决于您的 GlobalData 项，您应该将其移至缓存中并在其中设置适当的依赖项，以便您将受益于“级联过期”。
即使您确实使用自定义缓存机制，您仍然必须提供所有同步，因此您不会通过避免其他机制来节省时间。
如果您需要（预先排序的）更改频率非常低的项目列表，您仍然可以通过使用 HttpRuntime 缓存来实现。因此，您可以只缓存一个字典，然后使用它来列出您的项目或通过您的自定义键进行索引和访问。