The database leader said it's buying the privately held server virtualization firm Xsigo Systems for an undisclosed sum. The 8-year-old company helps customers cut costs by allowing them to connect any server to any network. It counts British Telecom (BT), eBay (EBAY) and Verizon Communications (VZ) among its customers. Oracle's (ORCL) purchase follows VMware's (VMW) $1.3 bil purchase of network virtualizer Nicira last week. Oracle shares fell 0.6% to 30.58.