Bug 180842 Config memory buffer size in data engine execution.
To tuning the performance, it is necessary for DtE to expose API for clients to config the size of memory it used to store the final result set. A new AppContext string, "org.eclipse.birt.data.cache.memory.size" is proposed. The new appcontext entry only accept positive integer as input, the unit of which would be MB.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/odi/IEventHandler.java
IBaseExpression getBaseExpr( String name );
	
	/**
	 * Get column mapping of current query defintion, inc. its subqueries.
	 * @return
	 */
	Map getAllColumnBindings();
	
	/**
	 * Get column mapping of current query definition. 
	 * 
	 * @return
	 */
	Map getColumnBindings();
	
	/**
	 * Get the ExecutorHelper instance bound to this IEventHandler.
	 * 
	 * @return
	 */
	IExecutorHelper getExecutorHelper();
	
	/**
	 * Bound an ExcutorHelper to this IEventHandler.
	 * 
	 * @param helper
	 */
	void setExecutorHelper( IExecutorHelper helper );
}