This post is meant to give SharePoint Administrators an deeper look into the Distributed Cache along with some links to other resources on the internet.
Background
SharePoint 2013 uses the AppFabric (Caching) by Microsoft. Read here for a background on AppFabric. AppFabric Caching stores serialised managed objects in a ‘cache cluster’. The cache cluster consists of one or more machines (Cache Hosts) that pool their available physical memory. This pooled memory is presented and used by SharePoint as a single source of caching memory.
How is it used in SharePoint
SharePoint uses the Distributed Cache to store data for very fast retrieval across all entities. The Distributed Cache service provides in-memory caching services to several features in SharePoint Server 2013. Some of the features that use the Distributed Cache service include:
· Newsfeeds
· Authentication
· OneNote client access
· Security Trimming
· Page load performance
In SharePoint Server 2013, there are several caches that exist, all of which depend on the Distributed Cache service.
Different caches that depend on the Distributed Cache service as indicated in the following table:
| Name | Cache name | |
| Login Token Cache | DistributedLogonTokenCache | |
| Feed Cache | DistributedActivityFeedCache | This cache stores activities and conversations for use by the feeds on a user’s My Site. |
| Last Modified Time Cache | DistributedActivityFeedLMTCache | This cache stores time stamp information for all Feed Cache entities |
| OneNote Throttling | DistributedBouncerCache | |
| Access Cache | DistributedAccessCache | |
| Search Query Web Part | DistributedSearchCache | |
| Security Trimming Cache | DistributedSecurityTrimmingCache | |
| App Token Cache | DistributedServerToAppServerAccessTokenCache | |
| View State Cache | DistributedViewStateCache | |
| Default Cache | DistributedDefaultCache | This cache can be used by any feature. |
Source: http://technet.microsoft.com/en-us/library/jj219700.aspx
Installation
AppFabric is a required component for SharePoint 2013 and is installed as part of the prerequisite installer. Thus each server automatically becomes part of the ‘cache cluster’. There is nothing to configure here as SharePoint does this automatically.
Farm Architecture – modes
Here is some terminology that will be useful when talking SharePoint architecture and topology:
There are two ‘modes’ for Distributed Cache – A collocated mode or a dedicated mode. The Distributed Cache is started and run on all WFE and APP servers by default. If you have over 10000 users, you should look into a dedicated server (dedicated mode) Distributed Cache. Dedicated Mode simply means all other services are turned off and more memory is allocated to the Distributed Cache.
Farm design
While designing your topology, could consider starting the Distributed Cache service on your WFE servers (for redundancy) and stop the Distributed Cache Service on the APP server if you are concerned with ‘overhead’ caused by all the other services running on the APP server. You can consider a scale up plan if you are low on resources or scale out (by starting the Distributed Cache on other servers in the farm).
Finally it boils down to memory allocation at the end of the day. By default, the Distributed memory allocation size defaults to a value of 10 percent of total physical memory when SharePoint Server 2013 installs. You can change the memory allocation with the Update-SPDistributedCacheSize cmdlet.
Here is a link that may help on the ‘right approach’: http://technet.microsoft.com/library/jj219572%28office.15%29.aspx (note the ‘Capacity planning for the Distributed Cache service’ section).
Management
The Distributed Cache service can be stopped or started via the Central Administration or via PowerShell.
Servers can be added or removed from the ‘Cache cluster’ too. When removing the server, the Distributed Cache service is stopped, then unregistered from the server. Unregistering the Distributed Cache service means that you will not see the Distributed Cache service listed on the Services on Server page in Central Administration. Adding a server means that you will see the Distributed Cache service listed on Services on Server page in Central Administration.
To add a server and start the service in PowerShell: Add-SPDistributedCacheServiceInstance
To remove a server and stop the service in PowerShell:
Remove-SPDistributedCacheServiceInstance
To stop (not remove) the Distributed Cache service by using Central Administration: In Central Administration, click Application Management. In Service Applications, click Manage Services on Server. On the Services on Server page, locate the Distributed Cache service. If the Distributed Cache service is started and you want to stop the service, under Action, click Stop.
To stop (not remove) the Distributed Cache service by using Windows PowerShell: At the Windows PowerShell command prompt, run the following command: $instanceName =”SPDistributedCacheService Name=AppFabricCachingService” $serviceInstance = Get-SPServiceInstance | ? {($_.service.tostring()) -eq $instanceName -and ($_.server.name) -eq $env:computername} $serviceInstance.Unprovision()
To check existing memory allocation of the Distributed Cache Host:
Use-CacheCluster
Get-AFCacheHostConfiguration -ComputerName ComputerName -CachePort “22233”
To reconfigure the cache size of the Distributed Cache Service:
Update-SPDistributedCacheSize -CacheSizeInMB CacheSize
Firewall configuration considerations
The Distributed Cache service uses the following communication ports:
22233
22234
22235
22236
Monitoring
The Distributed Cache can be monitored using below performance counters in Perfmon:
SharePoint Distributed Cache Counters
Cache Data Transferred Per Sec
Cache Hit Count
Cache Hit Ratio
Cache Miss Count
Cache Read Requests per sec
Cache Write Requests per sec
Total Cache Read Requests
Total Cache Write Requests
Additionally, there are three groups of ‘AppFabric’ counters available. Note there are multiple instances – indicating the different caches present in the Distributed Cache.
AppFabric Caching:Cache
AppFabric Caching:Host
AppFabric Caching:Secondary Host
Important Distributed Cache resource
Manage the Distributed Cache service in SharePoint Server 2013
Plan for feeds and the Distributed Cache service in SharePoint Server 2013
The above link shows how you can:
- Change the memory allocation of the Distributed Cache service
- Add or remove a server in a Distributed Cache cluster
- Perform a graceful shutdown of the Distributed Cache service
- Change the service account
- Repair a cache host
