Major expectation raised by user for SharePoint other then Search ,is to have Good User Experience and Faster in it operation.
In Order to improve SharePoint User experience, Microsoft added a new feature called Distributed Cache service, it cache frequently requested information and made it available quickly to all the servers(Web Front end) in the farm. Distributed Cache can be used for quick data retrieval. It stores data in memory and does not have a dependency on databases in SharePoint Server 2013.
It is mainly used to facilitate Search and the new social features in SharePoint 2013, as both of these require fast access to vast amounts of information.
Fast retrieval from the in-memory caching of Distributed Cache Service will lowering the load on SQL Server. It is a feature that will be used mainly by large SharePoint farms. . If you plan to use activity feeds, Distributed Cache service must be enabled on the Sharepoint Farm. This cache temporarily stores the microblog entries to make it immediately available to others in the environment.
Distributed Cache Service in SharePoint is the extension of Windows App Fabric which is a pre requisite in SharePoint 2013.
Benefit: Distributed Cache service holds context- and application specific information in memory, it eliminates the need to set the “sticky session” (or server affinity) on the network load balancer for SharePoint farms that have many SharePoint web Servers.
Why the need of sticky session is required in SharePoint 2010?
Distributed Cache Service cache login tokens . It is a big improvement over SharePoint 2010, which stored the login token on each Web front end server in the farm. “In SharePoint 2010, users who are redirected to a different load-balanced WFE often need to re authenticate when using SAML or FBA authentication if load balancer affinity, also called sticky sessions, is not enabled. Therefore, sticky sessions are no longer required with SharePoint 2013.”
Some of the features that use the Distributed Cache service:
➤ All social features
➤ Collaboration features
➤ OneNote client access
➤ Security trimming
➤ Page load performance
Note: Distributed Cache does not replace other “caches” within SharePoint, such as BLOB cache and Output cache as they are required specific to their need.
Server that is running the Distributed Cache service is called cache hosts. When one or more servers of the SharePoint farm runs the Distributed Cache service it create a Cache Cluster . The total cache size for the server farm is the sum of the memory allocated to the Distributed Cache service on each cache host. There is only ever one copy of an item in the cache. Data is not duplicated or copied on other cache hosts in the cache cluster. Therefore cache cluster cannot be configured for High Availability.
Distributed Cache service can be deployed in two modes:
1) Dedicated mode
2) Collocated mode.
In dedicated mode, No other service runs on SharePoint Services on Server other than Distributed Cache service . In collocated mode, Distributed Cache service runs along with other services on SharePoint server. It is always recommended to deploy Distributed Cache service in Dedicated mode.
Distributed Cache service is a memory intensive service. It is not recommended to run following services on same server running Distributed Cache service.: Search Services, Project Server service, SQL Server, Excel Services.
If a server running Distributed Cache Service (cache host) & the server utilization reaches 95%, DCS will start throttle itself and will no longer accept new read or write requests until the utilization falls below 70%. It doesn’t mean that user will not get their data, it means SharePoint will then request the information from the SQL server.
I will try to explain planning and Configuration of Distributed Cache service in my next article..
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