Single-User Mode

Version 8.51 of Extended Parallel Server adds a new single-user mode, in which only user informix can perform and log database operations. By starting a coserver in single-user mode, or by switching to single-user more from on-line mode, the DBSA can reduce the risk of concurrency effects from non-informix sessions, such as waits for locks, contention for resources, or errors caused by dirty readers or by locking during maintenance, migration, or other high-priority tasks. Unlike quiescent mode, single user-mode supports the full range of SQL operations and administrative utilities of Extended Parallel Server.

Note that this feature does not disable concurrency while the database server is in single-user mode. Rather, this mode restricts the database server to one or more sessions of a single user, namely user informix. Only user informix can connect and perform database work while the server instance is in single-user mode. The connection attempt fails with error message (-27100) if a client who is not user informix attempts to connect to a coserver that is in single-user mode.

This restriction applies to distributed DML operations that originate on another database server, as well as to local connections, including ODBC and XA clients. It does not apply, however, to connections between coservers. For example. if Coserver 1 is in single-user mode, but Coserver 2 is in on-line mode, a client can connect to Coserver 2 and then modify database objects on Coserver 1.