Windows Azure Caching: Difference between revisions

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an in-memory, distributed caching feature designed for Microsoft Azure applications. Caching was available as a part of the Windows Azure SDK. The Azure Managed Cache and In-Role Cache services were retired, and Microsoft recommended migration to Azure Redis Cache.

'''Windows Azure Caching''' is an in-memory, [[Distributed cache|distributed caching]] feature designed for [[Windows Azure]] applications<ref name=CachingMain>{{cite web|title=Caching in Windows Azure|url=http://msdn.microsoft.com/en-us/library/gg278356.aspx|work=MSDN Library|publisher=Microsoft|accessdate=12 February 2013}}</ref>. Caching is currently available as a part of the [http://www.windowsazure.com/en-us/develop/net/#/ Windows Azure SDK].

==Architecture==

Windows Azure Caching allows a cloud service to host Caching on a Windows Azure role.<ref name="CachingMain/">{{cite web |title=Caching in Windows Azure |url=http://msdn.microsoft.com/en-us/library/gg278356.aspx |accessdate=12 February 2013 |work=MSDN Library |publisher=Microsoft}}</ref> The cache is distributed across all running instances of that role. Therefore, the amount of available memory in the cache is determined by the number of running instances of the role that hosts Caching and the amount of physical memory reserved for Caching on each instance.<ref name=CachingCapacityPlanning>{{cite web|title=Capacity Planning Considerations for Windows Azure Caching|url=http://msdn.microsoft.com/en-us/library/hh914129.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>.

There are two deployment topologies for Caching:

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The following diagram shows Caching in a dedicated topology. The cloud service shown has three roles: Web1, Worker1, and Cache1. There are two running instances of each role. In this example, the cache is distributed across all instances of the dedicated Cache1 role.

[[File:Windows Azure Caching (Dedicated).jpg|Type=frame|Location=none|300px|Represents a running Windows Azure cloud service that uses Caching with a dedicated topology.]]

A dedicated topology has the advantage of scaling the caching tier independently of any other role in the cloud service.<ref name=CachingCacheCluster>{{cite web|title=About Windows Azure Caching, Cache Cluster|url=http://msdn.microsoft.com/en-us/library/hh914161.aspx#Concept_CacheClusters|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. For the best Caching performance, a dedicated topology is recommended because the role instances do not share their resources with other application code and services.<ref name=CachingDedicated/>.

===Co-located topology===

In a co-located topology, you use a percentage of available memory on existing web or worker roles for Caching.<ref name=CachingColocated/>.

The following diagram shows Caching in a co-located topology. The cloud service has two roles: Web1 and Worker1. There are two running instances of each role. In this example, the cache is distributed across all instances of the Web1 role. Because this role also hosts the web front-end for the cloud service, the cache is configured to use only a percentage of the physical memory on each instance of the Web1 role.

[[File:Windows Azure Caching (Co-located).jpg|Type=frame|Location=none|250px|Represents a running Windows Azure cloud service that uses Caching with a co-located topology.]]

A co-located cache is a cost-effective way to make use of existing memory on a role within a cloud service.<ref name=CachingColocated/>.

==Examples==

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===Configuration example===

In [[Visual_Studio|Visual Studio]], Caching is configured in the Caching tab of the properties of the role that hosts Caching.<ref name=CachingHowToGuide>{{cite web|title=How to Use Windows Azure Caching|url=http://www.windowsazure.com/en-us/develop/net/how-to-guides/cache/|work=Windows Azure Website|publisher=Microsoft|accessdate=13 February 2013}}</ref>. This makes underlying changes to the ServiceConfiguration.cscfg file.<ref name=CachingCsCfg>{{cite web|title=Windows Azure Caching Role Configuration Settings (ServiceConfiguration.cscfg)|url=http://msdn.microsoft.com/en-us/library/jj658975.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. These settings determine the topology used (dedicated or co-located) and the number of named caches<ref name=NamedCaches>{{cite web|title=About Windows Azure Caching, Named Caches|url=http://msdn.microsoft.com/en-us/library/hh914161.aspx#Concept_NamedCaches|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref> and their settings.

Other roles must be configured to use Caching.<ref name=CacheClientConfig>{{cite web|title=Getting Started with Development for Windows Azure Caching, Configure the Clients|url=http://msdn.microsoft.com/en-us/library/hh914150.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. One way to do this is with a [[NuGet]] package. This includes modifying the web.config to contain a properly configured dataCacheClients<ref name=dataCacheClients>{{cite web|title=Windows Azure Caching Client Configuration Settings (Web.config), dataCacheClients|url=http://msdn.microsoft.com/en-us/library/jj658973.aspx#dataCacheClients|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref> section. The following example dataCacheClients section specifies that the role that hosts Caching is named “CacheWorker1”.

<syntaxhighlight lang=XML>

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===Code examples===

''Note that the code samples in this section are shown in [[C_Sharp_C Sharp (programming_languageprogramming language)|C#]].''

When hosting Caching on roles, the '''DataCache''' class constructor can be used to specify both the named cache and the '''dataCacheClient''' section for the cache client settings. The following code shows how to create a named cache, ''NamedCache2'', using the settings from a '''dataCacheClient''' section named ''customClient''.

<syntaxhighlight lang=CSharp"csharp">

DataCachevar Cachecache = new DataCache("NamedCache2", "customClient");

</syntaxhighlight>

The following method shows how to use the ''Cache'' object to retrieve data from the cache. In this example, a user identifier (''userid'') is the key for the associated user information object. The code first attempts to get this user information from the cache using the ''userid'' key. If that does not succeed, the code retrieves the information with a database query and then stores the returned user data in the cache. The next time the same code is run, the user information will be returned from the cache rather than the database. This assumes that the cached data has not been expired or evicted.

<syntaxhighlight lang=CSharp"csharp">

dataType get_user_dataGetUserData(string useriduserId) {

{

/* first try the cache */

dataType data = (dataType)cache.Get(userid) null;

if (!data) {

// Attempt to retrieve the user data from the cache:

/* not found : request database */

object dataObject = Cache.Get(userId);

data = db_select("SELECT * FROM users WHERE userid = ?", userid);

/* then store in cache until next get */

if (dataObject != null)

Cache.Add(userid, data);

data = (dataType)dataObject;

else

{

// If it doesn't exist in the cache, retrieve it from the database:

data = db_selectGetUserDataFromDatabase("SELECT * FROM users WHERE useriduserId = ?@userId", useriduserId);

// Put the returned data in the cache for future requests:

Cache.Add(useriduserId, data);

}

return data;

}

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The following method shows how to update data that is already in the cache.

<syntaxhighlight lang=CSharp"csharp">

void update_user_dataUpdateUserData(string useriduserId, stringdataType dbUpdateStringdata) {

{

/* first update database */

// Update the user information in the database:

result = db_execute(dbUpdateString);

result = UpdateUserDataInDatabase(userId, data);

if (result) {

/* database update successful : fetch data to be stored in cache */

if (!dataresult) {

data = db_select("SELECT * FROM users WHERE userid = ?", userid);

{

/* then store in cache to support future get calls */

// If successfully updated, update the cache:

Cache.Put(useriduserId, data);

}

}

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The following call removes the item from the cache.

<syntaxhighlight lang=CSharp"csharp">

Cache.Remove(useriduserId);

</syntaxhighlight>

==Shared Caching==

Windows Azure Shared Caching provides caching as a managed service.<ref name=SharedCaching>{{cite web|title=About Windows Azure Shared Caching|url=http://msdn.microsoft.com/en-us/library/hh697519.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. Unlike co-located or dedicated topologies, the cache is not hosted on Windows Azure roles in a single cloud service deployment. Instead, the cache is provided as a multitenant service with usage quotas.<ref name=SharedCachingQuotas>{{cite web|title=Understanding Quotas for Windows Azure Shared Caching|url=http://msdn.microsoft.com/en-us/library/gg185683.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. The service is divided into tiers that range from 128 MB to 4 GB.<ref name=SharedCachingFAQ>{{cite web|title=Windows Azure Shared Caching FAQ|url=http://msdn.microsoft.com/en-us/library/hh697522.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. In addition to storage capacity, each tier provides increasing processor and network capabilities.<ref name=SharedCachingFAQ/>. Shared Caching provides a way for multiple cloud services to access the same cache.

==History==

Windows Azure Caching has its roots in an on-premises technology, [[AppFabric]]. It was originally released as one of several Windows Azure AppFabric services, but the AppFabric designation in Windows Azure has since been abandoned. Many of the assembly names, namespaces, and APIs are identical between Windows Azure Caching and AppFabric Caching.<ref name=CachingOnPremisesAndCloud>{{cite web|title=Differences Between Caching On-Premises and in the Cloud|url=http://msdn.microsoft.com/en-us/library/gg185678.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. The first release of Caching for Windows Azure in April 2011 provided caching as a managed service in Windows Azure.<ref name=Caching2011Release>{{cite web|title=Introducing the Windows Azure Caching Service|url=http://msdn.microsoft.com/en-us/magazine/gg983488.aspx|work=MSDN Magazine|publisher=Microsoft|accessdate=13 February 2013}}</ref>. This offering is now called Shared Caching.

In October 2012, support was added for hosting Caching on roles within a cloud service deployment.<ref name=CachingRelNotes>{{cite web|title=Windows Azure Caching Release Notes (October 2012)|url=http://msdn.microsoft.com/library/jj651667.aspx|work=MSDN Library|publisher=Microsoft|accessdate=13 February 2013}}</ref>. This is now called WindowWindows Azure Caching.

==Related caching technologies==

Windows Azure Caching is related to other Microsoft caching technologies. These technologies share similar features, such as the assembly name, namespace, and types.<ref name=CachingOnPremisesAndCloud/>. However, there are some differences. The table below describes these technologies.

{| class="wikitable"

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! Caching Technology !! Target !! Installed By !! Description

|-

| [[AppFabric_Caching_Service|AppFabric Caching]] || [[On-premises_softwarepremises software|On-Premises]] || [[AppFabric]] || Distributed on-premises cache that uses servers that the user provisions and manages.

|-

| [[Windows Azure Caching#Architecture|Windows Azure Caching]] || [[Cloud_computingCloud computing|Cloud]] || [http://www.windowsazure.com/en-us/develop/net/#/ Windows Azure SDK] || Caching is distributed across the instances of a single role in a Windows Azure cloud service deployment.

|-

| [[Windows Azure Caching#Shared Caching|Windows Azure Shared Caching]] || [[Cloud_computingCloud computing|Cloud]] || [http://www.windowsazure.com/en-us/develop/net/#/ Windows Azure SDK] || Caching is provided as a multitenant service for use by Windows Azure cloud services.

|}

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* [http://msdn.microsoft.com/en-us/library/windowsazure/microsoft.applicationserver.caching Windows Azure Caching Class Library Reference]

{{Microsoft Azure Services Platform}}

[[Category:Cloud computing]]

[[Category:Microsoft cloud services]]

[[Category:Database caching]]

[[Category:Cache (computing)]]

[[Category:Software development]]