Absolute Data Expiration in Cache

NCache allows you to configure absolute expiration with your cache items. This will expire the items at the exact date and time specified by the client. Absolute expiration can be specified on items that are required for a limited time in the cache. For example, a company announces flash sale for 24 hours on certain products. These items can then be cached with an absolute expiration of 24 hours so they are expired from the cache as soon as the sale ends.

Moreover, this DateTime value is converted to UTC time to cater the case where the cache server and client are in different time zones. So the items will be expired at the exact time which has been specified by the user.

Note
  • To use Maven packages for NCache Professional Edition, change the <artifactId> as shown below:
    • <artifactId>ncache-professional-client</artifactId>
  • To use Node.js API in NCache Professional Edition, install and include the ncache-professional-client npm package in your Node.js application.

Pre-Requisites

Add/Update Item with Absolute Expiration

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

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.

The following example sets the value of the Expiration property to Absolute Expiration of 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:

  • "Cache Count" Counter in NCache Web Monitor or PerfMon Counters
  • Using cache.Contains() after expiration interval has elapsed
  • Using cache.Count before and after specifying expiration.
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
    var cacheItem = new CacheItem(product);

    // Set Expiration TimeSpan
    var expiration = new Expiration(ExpirationType.Absolute, TimeSpan.FromMinutes(5));

    cacheItem.Expiration = expiration;

    // Add/Update item with expiration
    cache.Insert(key, cacheItem);
}
catch (OperationFailedException ex)
{
    // Exception can occur due to:
    // Connection Failures 
    // Operation Timeout
    // Operation performed during state transfer
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Add/Update Item with Configured Default Expirations

Note

This feature is only available in NCache Enterprise Edition.

You can specify absolute expiration in the API using the DefaultAbsolute and DefaultAbsoluteLonger values configured in NCache Web 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 (DefaultAbsolute 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. Once the configured time has elapsed, the item is expired.

Important

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

Tip

You can monitor/verify expiration through:

  • "Cache Count" Counter in NCache Web Monitor or PerfMon Counters
  • Using cache.Contains() after expiration interval has elapsed
  • Using cache.Count before and after specifying expiration
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 cacheItem instance for product
    var cacheItem = new CacheItem(product);

    // Set Expiration type
    var expiration = new Expiration(ExpirationType.DefaultAbsolute);

    cacheItem.Expiration = expiration;

    // Add/Update item into the cache with default expiration
    CacheItemVersion version = cache.Insert(key,cacheItem);
}
catch (OperationFailedException ex)
{
    // Exception can occur due to:
    // Connection Failures 
    // Operation Timeout
    // Operation performed during state transfer
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Set Absolute Expiration to Existing Item

NCache also provides the flexibility to set Absolute expiration to an existing cache item without having to reinsert it to cache. This is done through CacheItemAttribute class, which has the AbsoluteExpiration property to be set against the cache item. This sets the exact data and time at which the item should be invalidated from the cache. The attribute is then set against the existing key of the item, using the UpdateAttributes method of ICache.

The following example sets the absolute expiration for an item that already exists within the cache with no expiration set. This requires no need of re-adding or re-inserting the item into the cache.

Tip

You can monitor/verify expiration through:

  • "Cache Count" Counter in NCache Web Monitor or PerfMon Counters
  • Using cache.Contains() after expiration interval has elapsed
  • Using cache.Count before and after specifying expiration
try
{
    // Pre-condition: Cache is already connected
    // Pre-condition: Item already exists in cache
    string key = "Product:1001";

    // Create a CacheItemAttribute for absolute expiration
    // and set its value to 5 seconds
    var attr = new CacheItemAttributes();
    attr.AbsoluteExpiration = DateTime.Now.AddSeconds(5);

    // Set Absolute Expiration of 5 seconds against existing key
    cache.UpdateAttributes(key, attr);
}
catch (OperationFailedException ex)
{
    // Exception can occur due to:
    // Connection Failures 
    // Operation Timeout
    // Operation performed during state transfer
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Additional Resources

NCache provides sample application for Absolute Expiration on GitHub.

See Also

Sliding Data Expiration in Cache
Cache Data Expiration
Named Tags
Data Dependency for Relationship in Cache