Besides, ASP. NET Cache

ASP. NET provides three main forms of cache: page-level output cache, user control-level output cache (or segment cache), and cache API. The advantage of output cache and fragment cache is that it is very easy to implement. In most cases, it is sufficient to use these two caches. The cache API provides additional flexibility (in fact, it is quite flexible) and can be used in applications.ProgramEach layer uses the cache.

Among the many features provided by ASP. NET, cache support is undoubtedly my favorite feature. I have a good reason to say so. Compared with ASP. all other features of. net, the cache has the greatest potential impact on the application performance, using the cache and other mechanisms, Asp. NET developers can accept the additional overhead when building a site using a control with a large overhead (for example, DataGrid), without worrying that the performance will be greatly affected. To maximize the use of caching in applications, you should consider implementing caching at all program levels.

Early cache; frequent Cache

You should implement caching at each layer of the application. Add cache support to the data layer, business logic layer, UI, or output layer. Memory is currently very cheap-therefore, implementing caching in the entire application in a smart way can greatly improve performance.

Caching can mask many system design mistakes

Caching is a way to achieve "good enough" performance without much time and analysis. The memory is very cheap now, so if you try to optimize it by caching the output for 30 seconds instead of spending a whole day or even a weekCodeOr the database can obtain the required performance, and you will definitely select the cache solution (assuming you can accept 30 seconds of old data ). Cache is one of the features that get a 20% return Using 80%. Therefore, to improve performance, you should first think of cache. However, if the design is poor, it may lead to adverse consequences. Therefore, you should, of course, try to design the application correctly. However, if you only need to obtain high performance immediately, the cache is your best choice. You can redesign the application as soon as you have time.

Page-level output Cache

As the simplest form of caching, the output cache only retains the HTML copies sent in response to the request in the memory. Later, when there is another request, the cache output will be provided until the cache expires. In this way, the performance may be greatly improved.
To implement the page output cache, you only need to add an outputcache command to the page.
<% @ Outputcache duration = "60" varybyparam = "*" %>
Like other page commands, this command should appear at the top of the ASPX page, that is, before any output. It supports five attributes (or parameters), of which duration varybyparam is required.

 Segment cache, user control output Cache

Caching the entire page is usually not feasible because some parts of the page are customized for users. However, the rest of the page is shared by the entire application. These parts are most suitable for cache using fragment caching and user controls. Menu and other layout elements, especially those dynamically generated from the data source, should also be cached in this way. If necessary, you can configure the Cache control to be changed based on changes to its control (or other attributes) or any other changes supported by the page-level output cache. Using hundreds of pages of the same control group can also share the cache entries of those controls, rather than retaining a separate Cache version for each page.
The syntax used by fragment caching is the same as that used by page-level output caching, but it is applied to user controls (. ascx files) instead of web forms (. aspx files ). In addition to the location attribute, user controls also support all attributes supported by outputcache on web forms. The user control also supports the outputcache attribute named varybycontrol, which changes the control's cache according to the value of the user control (usually the control on the page, for example, dropdownlist) member. If varybycontrol is specified, You can omit varybyparam. Finally, by default, each user control on each page is cached separately. However, if a user control does not change with the page in the application and the same name is used on all pages, you can apply the shared = "true" parameter, this parameter allows the cached version of the user control to be used by all pages that reference the control.
Cache API, Using Cache objects

Page-level and user control-level output cache is indeed a way to quickly and easily improve site performance, but in ASP. net, the real flexibility and powerful functions of the cache are provided by the cache object. With cache objects, you can store any serializable Data Objects and control the expiration method of cache entries based on the combination of one or more dependencies. These dependencies can include the time since the item was cached, the time since the item was last accessed, changes to files and/or folders, and changes to other cache items, after slight processing, you can also include changes to specific tables in the database.

In CacheMedium storage data

The simplest way to store data in a cache is to assign values to a key, just like a hashtable or dictionary object:

Cache ["key"] = "value ";

This method stores items in the cache without any dependencies, so it does not expire unless the cache engine deletes the items to provide space for other cached data. To include specific cache dependencies, you can use the add () or insert () methods. Each method has several reloads. The only difference between add () and insert () Is that add () returns a reference to a cached object, while insert () does not return a value (null in C, in VB ).

Example

 
Cache. insert ("key", myxmlfiledata, new system. Web. caching. cachedependency (server. mappath ("users. xml ")));
 

In this example, the XML data in the file can be inserted into the cache, without reading from the file in future requests. Cachedependency is used to ensure that the cache expires immediately after the file is changed, so that the latest data can be extracted from the file and cached again. If the cached data comes from several files, you can also specify an array of file names.

 
Cache. insert ("dependentkey", mydependentdata, new system. Web. caching. cachedependency (New String [] {}, New String [] {"key "}));
 

In this example, the second data block with the key value "key" can be inserted (depending on whether the first data block exists ). If a key named "key" does not exist in the cache, or if the item associated with the key expires or is updated, the cache entry of "dependentkey" expires.

Cache. insert ("key", mytimesensitivedata, null, datetime. Now. addminutes (1), timespan. Zero );
 

Absolute Expiration: In this example, the cache will be cached for one minute, and the cache will expire after one minute. Note: the absolute expiration and sliding expiration (see below) cannot be used together.

 
Cache. insert ("key", myfrequentlyaccesseddata, null, system. Web. caching. cache. noabsoluteexpiration, timespan. fromminutes (1 ));
 

Sliding Expiration: This example caches frequently used data. The data will be kept in the cache until it has not been referenced for up to one minute. Note: slide expiration and absolute expiration cannot be used together.

More options

In addition to the dependencies mentioned above, we can also specify the priority of items (low, high, notremovable in sequence, they are in the system. web. caching. defined in cacheitempriority enumeration) andCacheitemremovedcallbackFunction. Most of the time, the default priority is enough-the cache engine can normally complete tasks and handle cache memory management. The cacheitemremovedcallback option takes into account some interesting possibilities, but in fact it is rarely used. However, to illustrate this method, I will provide an example of its usage:

CacheitemremovedcallbackExample

System. web. caching. cacheitemremovedcallback callback = new system. web. caching. cacheitemremovedcallback (onremove); cache. insert ("key", myfile, null, system. web. caching. cache. noabsoluteexpiration, timespan. zero, system. web. caching. cacheitempriority. default, callback );... public static void onremove (string key, object cacheitem, system. web. caching. cacheitemremovedreason reason) {appendlog ("the cached value with key'" + key + "'was removed from the cache. reason: "+ reason. tostring ());}
 

This example uses

 
Appendlog ()
 

Any logic defined by the method to record the reason for data expiration in the cache. When deleting items from the cache and recording the Reason for deletion, you can determine whether the cache is effectively used or whether you may need to increase the memory on the server. Note: callback is a static (shared in VB) method. We recommend that you use this method because if you do not use it, the instance of the class that saves the callback function will be kept in the memory, to support callback (not required for static/shared methods ).

This feature has a potential use-Refresh cached data in the background so that you never have to wait for data to be filled, but the data remains relatively new. But in fact, this feature is not applicable to the current version of the cache API, because the callback is not triggered or not completed before the cached items are deleted from the cache. Therefore, the user will frequently send a request to access the cache value, and then find that the cache value is empty and has to wait for the cache value to be refilled. I want to see an additional callback in future ASP. NET versions, which can be called cacheditemexpiredbutnotremovedcallback. If this callback is defined, it must be completed before deleting the cache item.

Cache Data Reference Mode

Whenever we try to access the data in the cache, we should consider a situation where the data may no longer be in the cache. Therefore, the following pattern should be applicable to your access to the cached data. In this case, we assume that the cached data is a data table.

 
Public datatable getcustomers (bool bypasscache) {string cachekey = "customersdatatable"; object cacheitem = cache [cachekey] As datatable; If (bypasscache) | (cacheitem = NULL )) {cacheitem = getcustomersfromdatasource (); cache. insert (cachekey, cacheitem, null, datetime. now. addseconds (getcachesecondsfromconfig (cachekey), timespan. zero);} return (datatable) cacheitem ;}
 

Note the following points about this mode:

• Some values (such as cachekey, cacheitem, and cache duration) are defined at one time and only once.

• You can skip the cache as needed-for example, when a new customer is registered and redirected to the customer list, the best way is to skip the cache and refill the cache with the latest data, this data includes newly inserted customers.

• The cache can only be accessed once. This method improves performance and ensures that nullreferenceexceptions does not occur because the item exists during the first check, but has expired before the second check.

• This mode uses the strong type check. The "as" Operator in C # tries to convert the object to the type. If the object fails or is empty, only null (null) is returned ).

• The duration is stored in the configuration file. Ideally, all cache dependencies (whether file-based, time-based, or other types of Dependencies) should be stored in the configuration file, this allows you to make changes and easily measure performance. We also recommend that you specify the default cache duration. If you do not specify the duration for the used cachekey, use the default duration for the getcachesecondsfromconfig () method.

• The related code example is a helper class, which will handle all the above cases, but allows one or two lines of code to access the cached data