A Shared Memory Access (SMA) server can be made highly available with the solidDB HotStandby (HSB) component.
In an SMA with HSB setup, there can be one or more SMA applications on each computer. The application connection to the database can be configured as a regular SMA connection (SMA Basic Connectivity) or as a Transparent Connectivity SMA connection (SMA TC). With both connectivity types, the application on the primary server uses an SMA connection to execute reads and writes locally, and the application on the secondary server uses an SMA connection to execute reads locally. Additionally, with an SMA TC connection, write transactions from the application on the secondary server can be executed on the primary server by using a network connection. Furthermore, if the load balancing option is enabled with the SMA TC connection, the applications can operate in an active-active manner; on each computer, the full functionality of database access is available.
The following diagram shows a pair of SMA servers that are configured as an HSB pair:
With SMA TC, the application on each computer must be able to connect to the local server by using an SMA connection and to the remote server by using a network-based connection.
Failover and switchover handling
▪ The connection handle is maintained during switchovers and failovers as long as one of the servers is in the PRIMARY ACTIVE, PRIMARY ALONE, or STANDALONE state.
▪ If the SMA server fails, the application might fail also. To ensure high availability in such a failure scenario, your system must include an application-level failover mechanism that moves the service offered by the application from the failed application instance to another instance.
