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/api/DataEngine.java
/**
     * @deprecated Use newDataEngine(Scriptable) instead. Home Dir is no longer used.
     */
    public static DataEngine newDataEngine( Scriptable sharedScope, File homeDir )
    {
        return newDataEngine( sharedScope );
    }
        
    /**
	 * If and only if current mode is DataEngineContext.MODE_PRESENTATION, query
	 * result can be retrieved from report document. Otherwise a BirtException
	 * will be thrown immediatelly.
	 * 
	 * @param queryResultID
	 * @return an instanceof IQueryResults
	 * @throws BirtException
	 */
	public abstract IQueryResults getQueryResults( String queryResultID )
			throws BirtException;
    
	/**
	 * Provides the definition of a data source to Data Engine. A data source
	 * must be defined using this method prior to preparing any report query
	 * that uses such data source. <br>
	 * Data sources are uniquely identified name. If specified data source has
	 * already been defined, its definition will be updated with the content of
	 * the provided definition object.
	 */
	abstract public void defineDataSource( IBaseDataSourceDesign dataSource ) 
			throws BirtException;