When you set hadr_peer_window to a
non-zero time value, then a HADR primary-standby database pair continues
to behave as though still in peer state, for the configured amount
of time, if the primary database loses connection with the standby
database. This helps ensure data consistency.
- Configuration type
- Database
- Parameter type
- Configurable
- Default [range]
- 0 [0 − 4 294 967 295]
- Unit of measure
- Seconds
- Usage notes:
- The value will need to be the same on both primary and standby
databases.
- A recommended minimum value is 120 seconds.
- When the hadr_syncmode value
is set to ASYNC or SUPERASYNC, the hadr_peer_window value
is ignored.
- To avoid impacting the availability of the primary database when
the standby database is intentionally shut down, for example, for
maintenance, the peer window is not invoked if the standby database
is explicitly deactivated while the HADR pair is in peer state.
- The TAKEOVER HADR command with
the PEER WINDOW ONLY option will launch a takeover
operation only if the HADR standby is presently inside the defined
peer window.
- The
takeover operation with the hadr_peer_window parameter
might behave incorrectly if the primary database clock and the standby
database clock are not synchronized to within 5 seconds of each other.
That is, the operation might succeed when it should fail, or fail
when it should succeed. You should use a time synchronization service
(for example, NTP) to keep the clocks synchronized to the same source.
- On the standby database, the peer window end time
is a time specified in the last heartbeat message that the standby
received from the primary database, and is not directly related to
when the standby detects loss of the connection.
DB2 Version 9.7 for Linux, UNIX, and Windows