Sliding Expiration in Cache

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 that 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's 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 the cache will be extended by another 10 minutes.

Prerequisites to Use Sliding Expiration in Cache

To learn about the standard prerequisites required to work with all NCache client-side features, please refer to the given page on Client-Side API Prerequisites.
For API details, refer to: ICache, CacheItem, CacheItemAttributes, Contains, Count, Expiration, Insert, UpdateAttributes.

Add/Update Item with Sliding Expiration

Note

This feature is also available in NCache Professional.

You can add/update the cache items to set expiration, using the Insert method. The CacheItem is a custom class provided by NCache that 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 Sliding 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 the NCache Monitor or PerfMon Counters.
Using cache.Contains after the expiration interval has elapsed.
Using cache.Count before and after specifying the expiration.

// Precondition: 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.Sliding, TimeSpan.FromMinutes(5));

cacheItem.Expiration = expiration;

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

// Precondition: 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.getProductID();

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

// Set Expiration type and TimeSpan
Expiration expiration = new Expiration(ExpirationType.Sliding, TimeSpan.FromMinutes(5));

cacheItem.setExpiration(expiration);

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

# Precondition: Cache is already connected
# Get product from database
product = fetch_product_from_db()

# Generate a unique cache key for this product
key = "Product:" + product.get_product_id()

# Create a new CacheItem for this product
cache_item = ncache.CacheItem(product)

# Set Expiration type and TimeSpan
expiration = ncache.Expiration(ncache.ExpirationType.SLIDING, ncache.TimeSpan.from_minutes(5))

cache_item.set_expiration(expiration)

# Add / Update item in cache with expiration
cache.insert(key, cache_item)

// This is an async method
// Precondition: Cache is already connected
// Get product from database against given product ID
var product = this.fetchProductFromDB(1001);

// Generate a unique cache key for this product
var key = "Product:" + product.getProductID();

// Create a new CacheItem for this product
// You also need to specify the FQN (Fully Qualified Name) of the class
var cacheItem = new ncache.CacheItem(product,"FQN.Product");

// Set Expiration type and TimeSpan
var expiration = new ncache.Expiration(ncache.ExpirationType.Sliding, ncache.TimeSpan.FromMinutes(5));

cacheItem.setExpiration(expiration);

// Add/Update item in cache with expiration
await this.cache.insert(key, cacheItem);

Add/Update Item with Configured Default Expirations

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

The following code associates the configured Default Expiration (DefaultSliding in this case) with an item, adds it to the cache if the key does not exist in the 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 the NCache Management Center or config.ncconf. If you pass the API for default expiration and it is not configured through the NCache Management Center or config.ncconf, it will not work.

// 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 TimeSpan
var expiration = new Expiration(ExpirationType.DefaultSliding);

cacheItem.Expiration = expiration;

// Add/Update item into the cache with expiration
CacheItemVersion version = cache.Insert(key, cacheItem);

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

// Generate a unique cache key for this product
String key = "Product:" + product.getProductID();

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

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

cacheItem.setExpiration(expiration);

// Add/Update item into the cache with expiration
CacheItemVersion version = cache.insert(key, cacheItem);

# Get product from database
product = fetch_product_from_db()

# Generate a unique cache key for this product
key = "Product:" + product.get_product_id()

# Create a new CacheItem for this product
cache_item = ncache.CacheItem(product)

# Set Expiration type and TimeSpan
expiration = ncache.Expiration(ncache.ExpirationType.DEFAULT_SLIDING)

cache_item.set_expiration(expiration)

# Add/Update item in cache with expiration
version = cache.insert(key, cache_item)

// This is an async method
// Get product from database against given product ID
var product = this.fetchProductFromDB(1001);

// Generate a unique cache key for this product
var key = "Product:" + product.getProductID();

// Create a cacheItem instance for product
// You also need to specify the FQN(Fully Qualified Name) of the class
var cacheItem = new ncache.CacheItem(product,"FQN.Product");

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

cacheItem.setExpiration(expiration);

// Add/Update item into the cache with expiration
var version = await this.cache.insert(key, cacheItem);

Additional Resources

NCache provides a sample application for Sliding Expiration on GitHub.