As with any new technology, time is needed for development and experience in tuning for good performance and acceptable stability. Recall, again, that Teradata has been providing massively parallel systems running a proprietary DBMS since 1984. The major DBMS vendors embarked on their versions towards the end of the 80s.
When used for decision support, parallel databases provide excellent results. On the other hand, their use for transaction processing has been less satisfactory.
The difficulty in obtaining a suitable scalability in transaction processing (a much larger portion of the market than decision support) explains their limited success. This is a real-world example of the difficulties faced in writing software for massively parallel architectures.
Source of Information : Elsevier Server Architectures 2005