Object-oriented data handling and OODB operation of LHD mass data acquisition system

The new data acquisition system of large helical device (LHD) diagnostics, i.e. LABCOM system, has successfully started its operation in March 1998. It has a simple but massive parallel-processing (MPP) structure by means of multiple PC/Windows NT environment, and the most significant methodology adopted for it is the object-oriented (OO) data handling through the whole system. The functions and data substances of the acquisition system are described in autonomous objects with the corresponding C++ class definitions. The object-oriented database management system (ODBMS) will be the only solution to provide a vast and virtual storage space for storing an enormous number of archiving data objects. Commercial ODBMS product 'O2' are installed on each diagnostic acquisition computer. Practical O2 investigations showed 300-400 kB/s as the data storing rate, whereas the data transfer rate from CAMAC digitizers to the computer is up to 700 kB/s in this system. Applying the GNU project's 'zlib' compression library for the data size reduction compensates this rate gap. Through the first and second (∼ no. 7132) LHD experimental campaigns, the LABCOM system acquired about 400 GB raw data, with maximum 120 MB per shot. These experiences proved that OO technology has great promise for the next generation of the data acquisition and storage system in fusion research experiments