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/impl/QueryExecutor.java
}
	/**
	 * Gets the Javascript scope for evaluating expressions for this query
	 * 
	 * @return
	 */
	public Scriptable getQueryScope( )
	{
		if ( queryScope == null )
		{
			 
			
			
			
			queryScope = newSubScope( parentScope );
			queryScope.setPrototype( dataSet.getJSDataSetObject( ) );
		}
		return queryScope;
	}
	/**
	 * Creates a subscope within parent scope
	 * @param parentAndProtoScope parent scope. If null, the shared top-level scope is used as parent
	 */
	private Scriptable newSubScope( Scriptable parentAndProtoScope )
	{
		if ( parentAndProtoScope == null )
			parentAndProtoScope = sharedScope;
		Context cx = Context.enter( );
		try
		{