Forced leader election

When the Election Leader detects an exception on the current server, it triggers a forced leader election. The following scenarios can trigger a forced leader election:

• CLOG_DISK_HANG: The CLOG disk is hung for more than 5 seconds. You can adjust the cluster parameter log_storage_warning_tolerance_time to modify this threshold.
• SLOG_WRITE_HANG: The thread for writing to the SLOG is hung for more than 5 seconds. You can adjust the cluster parameter data_storage_warning_tolerance_time to modify this threshold.
• SSTABLE_IO_HANG: The data disk is hung for more than 5 seconds. You can adjust the cluster parameter data_storage_warning_tolerance_time to modify this threshold.
• CLOG_DISK_FULL: The CLOG disk is full.
• SCHEMA_NOT_REFRESHED: The schema is not refreshed.

After the Election Leader detects an exception on the current server, it lowers its own election priority and selects a replica with a higher priority to trigger a re-election. You can query the DBA_OB_SERVER_EVENT_HISTORY view to view the forced leader election events and the corresponding exception reasons.

obclient(root@sys)[oceanbase]> select * from DBA_OB_SERVER_EVENT_HISTORY where module='FAILURE_DETECTOR' limit 10;

You can query the DBA_OB_SERVER_EVENT_HISTORY view to view the corresponding election events.

obclient(root@sys)[oceanbase]> select * from DBA_OB_SERVER_EVENT_HISTORY where module like '%ELECTION%' limit 10;