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/executor/cache/ResultObjectUtil.java
{
					ObjectInputStream ois = new ObjectInputStream( dis );
					try
					{
						obs[j] = ois.readObject( );
					}
					catch ( Exception e )
					{
						
					}
					ois.close( );
				}
			}
			rowDatas[i] = newResultObject( obs );
			rowDataBytes = null;			
			dis = null;
			bais = null;
		}
		return rowDatas;
	}
	/**
	 * Serialze result object array to file. The serialize procedure is
	 * conversed with de-serialize(read) procedure.
	 * 
	 * @param bos output stream
	 * @param resultObjects result objects needs to be deserialized
	 * @param length how many objects to be deserialized
	 * @throws IOException
	 */
	public void writeData( OutputStream bos,