Database Dependency Using Oracle

NCache provides OracleCacheDependency for notification based dependencies with Oracle. Internally, NCache uses OracleDependency to register data change notifications with the Oracle database server. Hence you need to understand the limitations and working mechanisms of OracleDependency while using this dependency. For example, limited sets of queries can be registered with OracleDependency. See Special Considerations Using Query Notifications and OracleDependency class for more detail.

Oracle Dependency is provided by NCache for synchronizing cache with Oracle database. Item expires if result of the command (based on command text) changes. Oracle Dependency is only available for Oracle database 10g release 2 or later. Also make sure that Oracle Data Providers for .NET (version 10.1.0.2.0 or later) is installed.

Configuring Notification on Oracle Server

NCache tracks changes in a database using notifications received from Oracle server about changes in the database. For this purpose, NCache registers CHANGE NOTIFICATION with the Oracle server. NCache server should have the CHANGE NOTIFICATION privileges to create a notification registration. If NCache server machine does not have these privileges, the following statement can be used to grant the CHANGE NOTIFICATION privilege to the user.

Adding Data with Oracle Dependency

The following code shows how to add data with OracleCacheDependency. Altering data after addition with Oracle Dependency will remove it from cache.

To utilize the API, include the following namespace in your application: Alachisoft.NCache.Runtime.Dependencies.

  //Create object to be added with dependency
  Product product = new Product();
  product.ProductID = 1001;
  product.ProductName = "Chai";
  string key = "Product:" + product.ProductID;
  try{   
       //Creating OracleCacheDependency
      string connectionString = "User Id=scott;Password=tiger;Data Source=oracle";
      string query = "SELECT rowID, productID FROM dbo.Products WHERE productID = 1001";

      OracleCacheDependency oracleDependency = new OracleCacheDependency(connectionString, query);

      //Adding cache item "Product:1001" with SqlDependency
      cache.Insert(key, product, oracleDependency, Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration, CacheItemPriority.Normal);

      //Modify Product record in database while program waits...
      Thread.Sleep(5000);

      //... and then check for its existence
      Object item = cache.Get(key);
      if (item == null){
            // item removed successfully
      }
      else{
            // item not removed successfully
      }
  }
  catch (OperationFailedException e){ }

In Oracle 10g, database change notifications are only object based. This means that change notifications will be fired if any row is modified in an object. Therefore, it is recommended to check rowID to confirm if the altered row is the one for which the event was registered. RowIDs cannot be retrieved unless explicitly included in query. So the user has to specifically include rowID in the query that is being registered with OracleDependency, otherwise the change notification will be fired if any row is modified in table.

When rowID is included in a query such as – Select rowID, productID, productname, unitprice from Products where ProductID = 220 - NCache will save the rowIDs of rows for which the change notification is registered. When it receives any change notification, NCache will compare the rowIDs to determine whether the row changed is the one for which the rowID is registered. Otherwise NCache will have no way to check against this and items for which change notification is registered may be removed if any row in the table changes.

In Oracle 11g, both object based and query based (default) notifications are provided. In query based notifications, change of the modified row will be notified only if the change notification is registered for it.