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CHAPTER 14 CONNECTION POOLING AND CACHING
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class DemoOracleConnectionCache { public static void main(String args[]) throws Exception { We instantiate the cache object and set the properties that define the limits and attributes of the cached connections. We also print the default cache scheme. OracleConnectionCacheImpl occi = new OracleConnectionCacheImpl(); occi.setURL ( "jdbc:oracle:thin:@rmenon-lap:1522:ora92" ); occi.setUser("scott"); // username occi.setPassword("tiger"); // password occi.setMaxLimit( 3 ); // max # of connections in pool occi.setMinLimit( 1 ); // min # of connections in pool System.out.println( "By default, the cache scheme is: " + occi.getCacheScheme() ); We then set the cache scheme to dynamic and invoke the method getOneMoreThanMax Connections(). We will see the definition of this method soon, but as the method name suggests, it attempts to get one connection more than the maximum limit of three set previously. This is to see how different cache schemes behave when the limit is exceeded. occi.setCacheScheme( OracleConnectionCacheImpl.DYNAMIC_SCHEME ); int maxLimit = occi.getMaxLimit(); System.out.println( "Max Limit: " + maxLimit ); System.out.println( "Demo of dynamic cache scheme - the default" ); _getOneMoreThanMaxConnections( occi, maxLimit ); We do the same for the cache scheme fixed return null : System.out.println( "\nDemo of fixed return null cache scheme" ); occi.setCacheScheme( OracleConnectionCacheImpl.FIXED_RETURN_NULL_SCHEME ); _getOneMoreThanMaxConnections( occi , maxLimit); }// end of main The method getOneMoreThanMaxConnections() is defined at the end of the program. It simply loops through and tries to create one more than the maximum limit passed to it as a parameter. private static void _getOneMoreThanMaxConnections( OracleConnectionCacheImpl occi , int maxLimit) throws SQLException { //Create an array of connections 1 more than max limit Connection[] connections = new Connection[ maxLimit + 1 ]; for( int i=0; i < connections.length; i++ ) { System.out.print( "Getting connection no " + (i+1) + " ..." );
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CHAPTER 14 CONNECTION POOLING AND CACHING
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connections[i] = occi.getConnection(); if( connections[i] != null ) System.out.println( " Successful." ); else System.out.println( " Failed." ); } // close all connections for( int i=0; i < connections.length; i++ ) { JDBCUtil.close( connections[i] ); } }// end of getOneMoreThanMaxConnections }// end of program The following is the output of the program when I ran it on my machine: B:\>java DemoOracleConnectionCache By default, the cache scheme is: 1 Max Limit: 3 Demo of dynamic cache scheme - the default Getting connection no 1 ... Successful. Getting connection no 2 ... Successful. Getting connection no 3 ... Successful. Getting connection no 4 ... Successful. Demo of Getting Getting Getting Getting fixed return null cache scheme connection no 1 ... Successful. connection no 2 ... Successful. connection no 3 ... Successful. connection no 4 ... Failed.
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As shown, even though we hit the maximum limit, we still got a connection successfully when the cache scheme was dynamic (which is the default). When the cache scheme was fixed return null, we got a null object when we tried to get a fourth connection. The fixed wait cache scheme isn t shown, but if you modify the program to use it, the program will wait forever when you try to get the fourth connection. This concludes our discussion of Oracle9i connection pooling and caching. It s time now to look at the implicit connection caching of Oracle 10g.
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CHAPTER 14 CONNECTION POOLING AND CACHING
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Oracle 10g Implicit Connection Caching
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As mentioned earlier, starting with Oracle 10g, the cache architecture just discussed was deprecated. It has been replaced by a more powerful, JDBC 3.0 compliant implicit connection caching. The highlights of implicit connection caching are Transparent access to a connection cache at the data source level. Support for connections with different usernames and passwords in the same cache. Ability to control cache behavior by defining a set of cache properties. The supported properties include ones that set timeouts, the maximum number of physical connections, and so on. Ability to retrieve a connection based on user-defined connection attributes (a feature known as connection striping). Ability to use callbacks to control cache behavior When a connection is returned to the cache. When a connection has been abandoned. When an application requests a connection that does not exist in the cache. The new class OracleConnectionCacheManager is provided for administering the connection cache. With the new cache architecture, you can turn on connection caching simply by invoking setConnectionCachingEnabled( true ) on an OracleDataSource object. After caching is turned on, the first connection request to OracleDataSource implicitly creates a connection cache. There is a one-to-one mapping between the OracleDataSource object and its implicit connection cache.
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