Using Write-Behind with Cache Operations

Note

This feature is only available in NCache Enterprise Edition.

This section explains the use of Write-Behind mode after deploying and configuring Write-Through provider. Write-Behind updates the data source asynchronously after updating the cache store.

Important

For Java, before deploying your JAR files, you need to make sure that:

• JDK 11 is installed.
• Environment variable for Java is set.

Prerequisites

• .NET/.NET Core
• Java

• Install the Alachisoft.NCache.SDK NuGet package in your application.
• To utilize the APIs, include the following namespaces in your application:
  • Alachisoft.NCache.Runtime.DatasourceProviders
  • Alachisoft.NCache.Runtime.Caching
  • Alachisoft.NCache.Client
  • Alachisoft.NCache.Runtime.Exceptions
• Cache must be running.
• The application must be connected to cache before performing the operation.
• Make sure that the data being added is serializable.
• For API details refer to: CacheItem, Get, Insert(), IWriteThruProvider, Remove, InsertBulk(), RemoveBulk(), InsertAsync(), RemoveAsync().
• To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.
• To handle any unseen exceptions, refer to the Troubleshooting section.

Add/Update with Write-Behind

You can add/update cache items with or without callback in the cache along with Write-Behind enabled. Adding with callback notifies you on the type of event occurred which you register.

Add without Callback Method

The following example adds an item in the cache with Write-Behind enabled, using the Insert() method. Using this method, if an item is already present in the cache, the new value overwrites the old value.

• .NET/.NET Core
• Java

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

  // Specify the key of the cacheItem
  Product product = FetchProductByProductID(1001);
  string key = $"product:ProductID";
  var cacheItem = new CacheItem(product);

  // Enable write through for the cacheItem created
  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;

  // Add item in the cache with write-behind  
  cache.Insert(key, cacheItem, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // 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 with Callback Method

The following example adds an item in the cache with callback registered and event type of ItemAdded with Write-Behind enabled.

• .NET/.NET Core
• Java

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

  // Specify the key of the cacheItem
  Product product = FetchProductByProductID(1001);
  string key = $"product:ProductID";
  var cacheItem = new CacheItem(product);

  // Enable write through for the cacheItem created
  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemAdded);

  // Add item in the cache with write-behind  
  cache.Insert(key, cacheItem, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}
private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}

Remove Existing Data with Write-Behind

The following example removes the item from the cache with Write-Behind enabled, using the Remove method, corresponding to the key provided as well as from the data source and registers the events for the operation.

• .NET/.NET Core
• Java

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

  // Specify the key of the item
  string key = "Product:1001";

  // Enable write through for the cacheItem created
  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemRemoved);

  // Remove the item corresponding to the key with write-through enabled
  cache.Remove(key, null, null, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}
private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}

Bulk Operations

Add/Update Bulk Items with Write-Behind

The following example adds bulk items in the cache with Write-Behind enabled, using the InsertBulk() method. If the items are already present in the cache, new values overwrite the existing values.

• .NET/.NET Core
• Java

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

  // Fetch all products from database
  Product[] products = FetchProductsFromDB();

  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemAdded);
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemUpdated);

  IDictionary<string, CacheItem> dictionary = new Dictionary<string, CacheItem>();

  foreach(var product in products)
  {
    string key = $"Product:{product.ProductID}";
    var cacheItem = new CacheItem(product);

    dictionary.Add(key, cacheItem);
  }
  IDictionary<string, Exception> keysFailedToUpdate = cache.InsertBulk(dictionary, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}

private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}

Remove Existing Items with Write-Behind

The following example removes a bulk of items from the cache with Write-Behind enabled, using the RemoveBulk() method.

• .NET/.NET Core
• Java

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

  // Get Keys
  Product[] products = FetchProductsFromDB();

  // Specify keys to remove from cache 
  string[] keys = new string[products.Length];
  int index = 0;

  foreach (var product in products)
  {
    keys[index] = $"Product:{product.ProductID}";
    index++;
  }

  // Create dictionary to store removed items
  IDictionary<string, Product> removedItems = new Dictionary<string,Product>();

  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemRemoved);

  // Remove items with write-behind enabled
  cache.RemoveBulk(keys, out removedItems, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}
private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}
protected void OnDataSourceItemsRemoved(IDictionary iDict)
{
  //Perform appropriate actions upon response
}

Note

Use the method OnDataSourceItemsRemoved() to perform operations after data removal from the cache.

Asynchronous Operations

Add/Update Item with Write-Behind

The following example adds item asynchronously in cache with Write-Behind enabled, using the InsertAsync() method.

• .NET/.NET Core
• Java

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}";
  var cacheItem = new CacheItem(product);

  // Enable write behind for the cacheItem created
  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemAdded);

  // Add Product object to cache
  Task task = cache.InsertAsync(key, cacheItem, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}

private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}

Remove Item with Write-Behind

The following example removes existing items asynchronously from the cache with Write-Behind enabled, using the RemoveAsync() method.

• .NET/.NET Core
• Java

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

  // Unique cache key of product to remove
  string key = $"Product:{product.ProductID}";

  // Enable write behind for the cacheItem created
  var writeThruOptions = new WriteThruOptions();
  writeThruOptions.Mode = WriteMode.WriteBehind;
  writeThruOptions.SetDataSourceNotification(DataSourceModifiedCallBack, EventType.ItemRemoved);

  // Asynchronously remove items from cache
  Task<Product> task = cache.RemoveAsync<Product>(key, writeThruOptions);
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
  }
}
catch (Exception ex)
{
  // Any generic exception like ArgumentNullException or ArgumentException
}
private void DataSourceModifiedCallBack(string key, WriteBehindOpResult result)
{
  // Perform appropriate actions upon response
}

Use Data Structures with Write-Behind

The following example uses different data structures with Write-Behind enabled, on the specified item.

• .NET/.NET Core
• Java

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

  // Specify the key of the item
  string key = "Product:1001";
  var dataTypeAttributes = new DataTypeAttributes();
  var writeThruOptions = new WriteThruOptions(WriteMode.WriteBehind, WriteThruProviderName);

  switch(mainMenu)
  {
    case mainMenu.GetDistributedCounter:
      // Modify or add count of the corresponding item with write thru enabled
      var distributedCounter = cache.DataTypeManager.CreateCounter("counter", dataTypeAttributes, 0, writeThruOptions);

      // perform operations on counter
      break;  
    case mainMenu.GetDistributedDictionary:
      // Modify or add dictionary of the corresponding item with write thru enabled
      var distributedDictionary = cache.DataTypeManager.CreateDictionary<string, int>(key, dataTypeAttributes, writeThruOptions);

      // perform operations on dictionary
      break;
    case mainMenu.GetDistributedList:
      // Modify or add the list of the corresponding item with write thru enabled
      var distributedList = cache.DataTypeManager.CreateList<int>("list", dataTypeAttributes, writeThruOptions);

      // perform operations on list
      break;
    case mainMenu.GetDistributedQueue:
      // Modify or add the queue of the corresponding item with read thru enabled  
      var distributedQueue = cache.DataTypeManager.CreateQueue<int>("queue", dataTypeAttributes, writeThruOptions);

      // perform operations on queue
      break;
    case mainMenu.GetDistributedHashSet:
      // Modify or add the HashSet of the corresponding item with read thru enabled
     var distributedHashSet = cache.DataTypeManager.CreateHashSet<int>("hashset", dataTypeAttributes, writeThruOptions); 

      // perform operations on hashset
      break;
  }  
}
catch (OperationFailedException ex)
{
  if (ex.ErrorCode == NCacheErrorCodes.BACKING_SOURCE_NOT_AVAILABLE)
  {
    // Backing source is not available
  }
  else if (ex.ErrorCode == NCacheErrorCodes.SYNCHRONIZATION_WITH_DATASOURCE_FAILED)
  {
    // Synchronization of data with backing source is failed due to any error
  }
  else
  {
    // 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 Write-Behind on GitHub.

See Also

Write-Through Provider Configuration and Implementation
Monitor Write-Through Counters
Configuring Write-Through Provider