Starting an Engine
If an engine unit starts before the governor, but after its partner has started, then it must negotiate with its partner to establish which unit is to become primary. If one unit has been marked as the preferred primary, then that unit becomes primary. If neither unit has been marked as the preferred primary, then the negotiation randomly determines which of the two becomes primary. If the governor starts up in the middle of this negotiation, the governor takes over and decides the issue. If the governor starts up after the negotiation is complete, the governor accepts the negotiated decision.
When an engine unit starts, it goes through an internal, transitional state (EMBRYONIC), then assumes one of two persistent states, ONLINE or STANDBY, depending on whether it is designated as the primary or backup engine unit. The STANDBY state is assumed immediately upon startup; however, the ONLINE state is achieved only after the engine unit has passed through a number of startup phases, such as logging on to the engine database and performing registrations with the Name Service. The startup phases are described in more detail below.
As a system manager you can override the state of an engine unit after it has started. For example, you can set the primary engine to a STANDBY state, and then set its partner to an ONLINE state, making the partner the new primary engine unit. The engine unit states are described below.
Engine unit state | Description |
|
|
EMBRYONIC | Internal, transitional startup state. |
ONLINE | Normal state of the primary engine unit. It is running, |
| connected to the engine database, and can accept client |
| sessions. |
STANDBY | Normal state of the backup engine unit. It is running, but is |
| not connected to the engine database and cannot accept client |
| sessions. |
|
|
Chapter 4 Managing Engines 107
