The market research group predicts that sales will grow to £14bn by 2006.
Although widespread IT spending cutbacks in 2001 left RDBMS vendors focusing on the middle market rather than high-end clients, the market will begin to mature as service providers start to ramp up their buying in 2004, IDC said.
Last year's tough economic climate has changed the market landscape. Some smaller vendors had to close down while industry stalwarts such as Progress Software were able to stay in the game, according to IDC.
Vendors with a solid track record in the middle market fared better than those dependent on large contracts, that were hit by cutbacks in spending and contract cancellations.
Microsoft thrived last year while Oracle slipped somewhat, although it continued to be the market leader, IDC noted.
Microsoft's success was based on the fact that the company's RDBMS software is fairly low-priced, has strong reseller channels, and sells to the middle market, according to Carl Olofson, application development and deployment research director at IDC.
Oracle, on the other hand, lost ground because much of its revenue is derived from high-end products sold to large accounts, Olofson said.
Meanwhile, IBM's growth was aided by the company's acquisition of Informix's RDBMS products.
The upswing in the RDBMS market will come as more online service providers seek to offer IT services over the Internet, Olofson said.
"Those vendors will need highly scalable and robust database software to be successful," he added.