Microsoft ASP.NET: An Overview of Caching

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Overview

Introduction to ASP.NET caching Output caching Data caching Difference between Data Caching and Output

Caching

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What is Caching

Cache = “secret store” Armies: cache weapons Squirrels: cache nuts Computers: cache data

Benefits of caching data: Reuse

Process once, reuse many times Faster, cheaper

Caching means temporary storage of data in memory that is highly-demanding and frequently used in order to accelerate performance and for quick access to various essential information. 

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Output Caching

What is output caching? @ OutputCache directive and the cache

object Output caching attributes:

Duration Location VaryByParam VaryByHeader VaryByCustom

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Output (or) Page Caching

This is the most simplest form of caching. caches the output of a page (or portions of it) so that content of page are not generated every time it is loaded.

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What Is Output Caching?

Pages that use the output cache are executed one time, and the page results are cached

The pre-executed page is then served to later requests

Performance and scalability both benefit Server response times reduced CPU load reduced

Appropriate caching of pages affects site performance dramatically

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@ OutputCache Directive and the Cache Object

@ OutputCache declaratively controls caching behavior For .aspx, .asmx, or .ascx

The cache object programmatically controls caching behavior

<%@ OutputCache Duration="600“ Location="Any“VaryByParm=“none” %>

Is equivalent to:[C#]Response.Cache.SetExpires(DateTime.Now.AddSeconds(600));Response.Cache.SetCacheability(HttpCacheability.Public);

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OutputCache Members: Duration and Location

Duration sets the time to cache the output In seconds Required

Location sets the location to cache the output Server: The output is held in memory on the Web server

and is used to satisfy requests Downstream: A header is added to the response to

indicate to proxy servers to cache the page Client: A header is added to the response indicating to

browsers to cache the page Any: Output cache can be located on any of these

locations None: No output caching is turned on for the item

<%@ OutputCache Duration="600" Location="Any“VaryByParam=“none” %>

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OutputCache Members: VaryByParam and VaryByHeader

VaryByParam This is a mandatory parameter. This is used to

mention whether variables in the request should result in separate cache entries.

“none" can be used to specify no separate cache requirement.

"*" indicates create a new cache entires for different set of variables.

<%@ OutputCache Duration="60" VaryByParam="none" %> 

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VaryByHeader , VaryByCustom

VaryByHeader and VaryByCustom are primarily used to customise look and feel of the on the client accessing site.

<%@ OutputCache Duration="60“ VaryByParam="None" VaryByCustom="browser" %> 

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Data Caching

What is data caching? How to insert objects into the cache Cache dependencies

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Data Caching

The basic principle of data caching is that you add items that are expensive to create to a special built in collection object

How to insert items into cache

Cache.Insert(key,dependencies,absoluteExpiration,_Slidingexpiration)

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Cache.Insert parametersParameter Description

Key A string that assigns a name to the cached item

Item The actual object that is to be cached

Dependencies A cache dependency object that allows you to create a dependency

absoluteExpiration A Datetime object representing the time at which the item will be removed from cache

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Parameter Description

slidingExpiration A Timespan object represents how long the ASP.NET will wait between requests before removing a cached item

Cache.Insert("student", ds, Nothing, DateTime.MaxValue, TimeSpan.FromMinutes(2))

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Cache dependency

Suppose a local XML file is cached into the cache object

Incase the XML file is updated and it needs to be reloaded once again but due to cache there may be latency

Cache dependencies overcomes this dilemma

It makes the object to drop from the cache the moment it is amended

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DatabaseCache

Browser

Data Caching

Data

Cache dependency

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Data Caching Output Caching

Data caching allows a web

application to store commonly used

objects so that they are available

for use across all pages in the site.

Page caching allows the server to

store a copy of the output of a

dynamic page, and to use this to

respond to requests instead of

running the dynamic code again.

Data caching is the storing of data

internal to a web application, such

that different pages can access the

data.

If you cache a page, you store a copy

of the output of the page

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Data Caching Output Caching

The data cache is available through the Cache property of either the Page or the HttpContext class

There are three approaches to setting page caching.

@OutputCache directive in the top of the ASP.NET page.

cache options via code.

The third option is to use meta data

attributes in code

Data remains in the cache for the time specified by the DateTime parameter of the Cache.Insert method

Pages remain in the cache for some length of time, determined by the Duration parameter. The value is set in seconds.

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Cache Dependencies

File-based dependencies Cached item invalidated when files change

Key-based dependencies Cached item invalided when another cached item

changes Time-based dependencies

Absolute time-based invalidations Sliding time-based invalidations

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Cache Dependency

File based dependency Key based dependency Time based dependency

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Key-based dependency invalidates a particular Cache item when another Cache item changes.

For example, if instead of loading our ProductData from a database, we loaded it from an XML file

Dim dom As XmlDocument() dom.Load(Server.MapPath("product.xml") Cache("ProductData") = dom

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Dim dependency as new CacheDependency(Server.MapPath("product.xml"))

Cache.Insert("ProductData", dom, dependency)

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Key based dependency

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Time based dependency

Time-based dependency simply expires the item at a defined point in time.We have two options for time based dependency Absolute—Sets an absolute time; for example,

current time + 10 minutes for the Cache entry to expire.

Sliding—Resets the time for the item in the Cache to expire on each request