The approach to highly available financial market data in the Sybase RAP - The Trading Edition system is the configuration of redundant components within a given Sybase RAP installation.
The incoming market data feed(s) from SIAC, NYSE, NASDAQ, and other sources have the ability to support redundant feeds, such that two or more processes can subscribe to these feeds, each of which receives identical data when all systems are running normally.
Feed handlers provided by third parties leverage this ability to support redundant feeds, and stress the necessity of providing both feed fault tolerance as well as feed handler fault tolerance.
Feed fault tolerance is provided by configuring the feed handler to subscribe to a pair of fault tolerant multicast data streams sent by the data providers (for example, SIAC and NASDAQ). If one of the data streams is interrupted, the feed handler continues to receive all of the data via the remaining data stream.
Feed handler fault tolerance is provided by implementing two feed handlers running in a hot standby mode using a heartbeat mechanism. A primary instance and a secondary instance process exactly the same data and maintain exactly the same internal state, but only the primary instance of a feed handler pair forwards market data to subscribing applications. In the event of a feed, feed handler, or feed handler hardware failure, the heartbeats cease and the secondary instance takes over as the primary instance. The new primary instance sends full record or order book images for all items that were modified just before the last heartbeat was received.
