DB2 10.5 for Linux, UNIX, and Windows
DB2 10.5 for Linux, UNIX, and Windows
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.
If you have not configured the hadr_target_list configuration parameter, the value for hadr_peer_window needs to be the same on both primary and standby databases. When hadr_target_list is set, the first standby listed (the principal standby) uses the primary's setting for hadr_peer_window and any setting for hadr_peer_window on the principal or auxiliary standbys is ignored unless one of them becomes the primary.
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. As a result, peer window is not supported in a DB2® pureScale® environment.
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 launches 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.