Windows velocity

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Open in new tab. Each cache host can run multiple named caches. These named caches can span across machines and are defined in configuration. Each named cache stores a logical group of data, such as a product catalog.

Named caches also set policies around availability, eviction, and expiration. Explicitly created regions—physically co-located data containers—may also exist within each named cache. As items are retrieved in bulk, regions become useful if the application consistently needs to address a group of cache items together. Additionally, these regions enhance usability by providing tag-based searching and enumeration of region cache items. Explicitly created regions are, however, an optional concept.

Velocity will implicitly create default regions behind the scenes if no region is explicitly specified. Lastly, within the implicitly and explicitly created regions are the cache items themselves, which are responsible for maintaining keys, objects, tags, timestamps, versions, and expiry data. Velocity currently supports two caching types: partitioned and local. Partitioned caches distribute cache items across the hosts for particular named caches.

Each overarching named cache can enable high availability, effectively causing Velocity to maintain a configurable number of backups for items within a named cache across machines in the Velocity tier. Local caching runs on the client to speed up access to data retrieved from Velocity. When local caching is used in concert with the Velocity partitioned caches, as data is retrieved from the Velocity server ring, cache items are stored in object form within the process running the Velocity client.

Further, as with server-side expiration policy, local caches can also each configure an expiration time for items. The Velocity configuration store consists of cache policies as well as the global partition map, which details the distribution of cache items across the cluster. Velocity uses the policies and global partition map defined within the configuration store to enforce the policies defined by named caches and to run the global partition manager, respectively. The global partition manager is a component of Velocity that is responsible for conveying the landscape of cache items to the rest of the cluster.

Clients ultimately utilize this information when communicating with the cluster to create routing tables that define correlations between data and Velocity service hosts. The global partition manager runs within one Velocity service host. If the host running the global partition manager goes down, another host within the Velocity cluster will assume responsibility by starting the global partition manager from the global partition map stored in the configuration store.

Velocity enables the configuration store to be placed on a network share or stored within SQL Server. To get started with Velocity, let's begin with an overview of the Velocity installation process, the initial cluster deployment, and a basic Velocity client application. Upon proceeding through the Velocity installer on a cache server, you are presented with the cache host configuration screen shown in Figure 5. The cache host configuration screen captures the cluster and service settings required to run your Velocity host.

First, this screen allows you to choose whether the configuration store is placed on a network share or stored within SQL Server. Next, the cluster is assigned a name as well as an approximate node size. The cluster size configuration is used to optimize performance within Velocity by tuning internal data structures according to your cluster size. It is possible to reset the cluster size at a later time as your cluster evolves. Finally, the service configuration values section captures the service port that the current host runs on, the port the cluster itself runs on, as well as the maximum amount of memory this Velocity host is to consume.

Click the Test Connection button to validate the connectivity of the configuration store. If the machine is running a firewall, make sure to allow the Velocity service through by adding an exception for DistributedCache. To install additional cache hosts, repeat these installation steps on new Velocity machines. When installing additional hosts, the cluster related settings will be detected automatically from the configuration store on the network share used during the installation of the first cluster host.

For this example, I installed a three-node cluster. Once Velocity is installed, it can be administered through Windows PowerShell. To start the Velocity command window, run the Velocity administration shortcut placed on the desktop after installation as administrator. To start the cache cluster, run the Start-CacheCluster command. The Get-CacheHost command will display the status of hosts across the cluster. Get-CacheStatistics will display cache item statistics for a particular named cache.

For more details on Velocity administration through Windows PowerShell, please see the documentation included with the Velocity installation. After joining cache hosts to the Velocity cluster, the XML policy configuration shown in Figure 6 is produced on the network share in the ClusterConfig.

The dcache configuration element represents the velsample cluster created during installation. This configuration section holds the policy configuration information that I set during the host installations, namely named caches, hosts, and configuration store settings.

In the caches element, Velocity automatically created a default, partitioned, named cache. This named cache configuration also holds the policy settings Velocity uses to enforce expiration and eviction settings that control how long cache items within this named cache should remain in memory as well as how Velocity removes these items once they expire.

In this default configuration, the defaultTTL value indicates that cache items will remain in memory for 10 minutes. In certain circumstances, it may be desirable to turn these expiration and eviction settings off. For example, in cases where the data set size is known to be relatively fixed, such as the product catalog in the example application. In this case, the eviction type would be set to none while the isExpirable setting would be set to false.

Next, in the hosts configuration element, each of the Velocity hosts specifies naming, size, and address information. Additionally, each host can act as a quorum host, or lead host. Lead hosts in Velocity are responsible for maintaining the stability of the cluster. These lead hosts collaborate to prevent split brain syndrome, a circumstance where a loss of communication within the cluster causes independently operating sub-clusters.

A majority of Velocity lead hosts must be running for the entire cluster to run, so it is critical to insulate your cluster with enough lead hosts to ensure a majority of these lead hosts do not fail simultaneously. There is some additional overhead involved in lead host communication. It is a good practice to run your cluster with as few lead hosts as necessary to maintain a quorum of leads.

For small clusters, ranging from one to three nodes in size, it is acceptable to run all nodes as lead nodes as the amount of additional overhead generated by a small grouping of lead hosts will be relatively low. For larger clusters, however, to minimize overhead involved in ensuring cluster stability, it is recommended to use a smaller percentage of lead hosts—for example, 5 lead hosts for a node cluster.

For my example app, to enable all three hosts to run as lead hosts, I can run a Stop-CacheCluster command, update the remaining quorumHost values to true, and then run Start-CacheCluster. Finally, the advancedProperties configuration element specifies the storage provider for and location of the partition map.

Here, the configuration specifies the network location of the partition map database. This partition map database is used by the host currently running the global partition manager.

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Check the system requirements included in the Velocity User Guide before installing. The Velocity Console is the administrative tool for the platform. Host profiles, scanner settings, custom keyboards, javascript scripts and custom client experiences are configured through this tool. Enabling Remote Work. Small and Medium Business. Humans of IT. Green Tech.

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