Sliding Expiration

NCache allows you to configure sliding expiration to retain the cache data as long as it is being used by the application and remove any data that has not been used for a specific period of time. This is particularly useful in maintaining sessions, as any session which has been idle for a specific period is considered inactive and can be removed by the cache.

Sliding expiration ensures that if the data is accessed within the specified time interval the cache item life span will be extended by the interval value. For example, a session is added with 10 minutes expiration. the session is accessed at the 6th minute, so the life of the session in cache will be extended by another 10 minutes.

Warning

You can not set both Sliding and Sliding expiration together for an item. If both expirations are passed, System.ArgumentException is thrown.

Pre-requisites For Using Expirations

  • Include the following namespace in your application:
    • Alachisoft.NCache.Web.Caching
    • Alachisoft.NCache.Runtime
  • The application must be connected to cache before performing the operation.
  • Cache must be running.
  • Make sure that the data being added is serializable.
  • To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Add/Update Existing Item with Sliding Expiration

You can add/update the cache items to set expiration, using the Insert method.

The following examples provide multiple ways of updating sliding expiration - these can be either user-specified values or the configured DefaultSliding and DefaultSlidingLonger values.

Important

Note that this API also specifies cache item priority for eviction, so the value for that parameter has been passed as Default, as it is not discussed here.

Add/Update Expiration Programmatically

You can specify sliding expiration in the API as a TimeSpan value. The following code associates sliding expiration with an item and adds it to the cache if the key does not exist in cache, and updates the item with expiration if the key exists. This item will expire after 5 minutes if not accessed within the duration, otherwise the item's life will be extended by another 5 minutes.

Tip

You can monitor/verify expiration through:

try
{
    // Pre-condition: Cache is already connected

    // Get product from database against given product ID
    Product product = FetchProductFromDB(1001);

    // Generate a unique cache key for this product
    string key = $"Product:{product.ProductID}";

    // Adding/Updating an item with sliding expiration of 5 minutes
    cache.Insert(key, product, Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(5), CacheItemPriority.Default);

    // Monitor/Verify expiration through either:
    // PerfMon Counters
    // cache.Contains(key)
    // cache.Count
}
catch (OperationFailedException ex)
{
    // NCache specific exception

    // Exception can occur due to:
    // Connection Failures
    // Operation performed during state transfer
    // Operation Timeout
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Configured Default Expirations

You can specify sliding expiration in the API using the DefaultSliding and DefaultSlidingLonger values configured in NCache Manager or config.ncconf. This provides flexibility of changing the value externally if needed, without changing the code.

The following code associates configured default expiration (DefaultSliding in this case) with an item and adds it to the cache if the key does not exist in cache, and updates the item with expiration if the key exists. If the item is not accessed within the configured time interval, the item will expire. Otherwise, the item's life will be extended by the same time interval.

Important

To enable default expiration, it is mandatory that you enable it through NCache Manager or config.ncconf. If you pass the API for default expiration and it is not configured through NCache Manager or config.ncconf, it will not work.

Tip

You can monitor/verify expiration through:

try
{
    // Pre-condition: Cache is already connected

    // Get product from database against given product ID
    Product product = FetchProductFromDB(1001);

    // Generate a unique cache key for this product
    string key = $"Product:{product.ProductID}";

    // Add/Update item with configured DefaultSliding expiration
    // You can use Cache.DefaultSlidingLonger, if configured
    cache.Insert(key, product, Cache.NoAbsoluteExpiration, Cache.DefaultSliding, CacheItemPriority.Default);

    // Monitor/Verify expiration through either:
    // PerfMon Counters
    // cache.Contains(key)
    // cache.Count
}
catch (OperationFailedException ex)
{
    // NCache specific exception

    // Exception can occur due to:
    // Connection Failures
    // Operation performed during state transfer
    // Operation Timeout
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Set Sliding Expiration with CacheItem

CacheItem is a custom class provided by NCache which can be used to add data to the cache and also lets you set additional metadata associated with an object of this class. This metadata defines the properties of the item like expiration, dependencies and more. You can refer to all properties of CacheItem here.

The following example sets the value of the SlidingExpiration property to 5 minutes for a CacheItem and adds it to the cache if the key does not exist - and updates the item if it exists.. This CacheItem will then be removed from the cache after 5 minutes.

Tip

You can monitor/verify expiration through:

try
{
    // Pre-condition: Cache is already connected

    // Get product from database against given product ID
    Product product = FetchProductFromDB(1001);

    // Generate a unique cache key for this product
    string key = $"Product:{product.ProductID}";

    // Create a new CacheItem for this product
    CacheItem cacheItem = new CacheItem(product);

    // Setting Sliding expiration of 5 minutes
    cacheItem.SlidingExpiration = TimeSpan.FromMinutes(5);

    // Add/Update item with expiration
    cache.Insert(key, cacheItem);

    // Monitor/Verify expiration through either:
    // PerfMon Counters
    // cache.Contains(key)
    // cache.Count
}
catch (OperationFailedException ex)     
{
    // NCache specific exception

    // Exception can occur due to:
    // Connection Failures
    // Operation performed during state transfer
    // Operation Timeout
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

See Also

Absolute Expiration
Cache Data Expiration
Named Tags
Data Relationship in Cache