缩减 OceanBase 集群及租户的高可用

# 检查 RS 历史任务记录，出现 tenant_balance_finished 说明数据删除已完成
# OceanBase V3.x 版本
select * from __all_rootservice_event_history order by gmt_create desc limit 10;
# OceanBase V4.x 版本
select * from DBA_OB_ROOTSERVICE_EVENT_HISTORY order by timestamp desc limit 10;

# 检查 server 状态，start 要晚于 offline 时间，状态为 active
# OceanBase V3.x 版本
select svr_ip, gmt_modified, zone, usec_to_time(start_service_time), usec_to_time(last_offline_time), status from __all_server;
# OceanBase V4.x 版本
SELECT svr_ip, zone, UNIX_TIMESTAMP(NVL(`start_service_time`, 0))*1000000 as start_service_time, status from DBA_OB_SERVERS;

# 检查数据副本是否补齐，<副本数>替换为预期副本数，返回为空说明已补齐
# OceanBase V3.x 版本
select /*+read_consistency(weak)*/ count(*)c from gv$partition group by table_id, partition_id having c != <副本数>;
# OceanBase V4.x 版本没有分区副本的概念，以下 SQL 检查日志流是否均有主，均有主则返回 0，表示正常
SELECT COUNT(1) FROM CDB_OB_LS A LEFT JOIN GV$OB_LOG_STAT B ON A.LS_ID = B.LS_ID AND A.TENANT_ID = B.TENANT_ID AND B.ROLE='LEADER' WHERE B.LS_ID IS NULL AND A.STATUS NOT IN ('CREATING', 'CREATED', 'TENANT_DROPPING', 'CREATE_ABORT', 'PRE_TENANT_DROPPING');

# 检查日志是否同步，返回为空说明已同步
# OceanBase V3.x 版本
select svr_ip, svr_port, table_id, partition_idx from __all_virtual_clog_stat where is_in_sync= 0 and is_offline = 0 and replica_type != 16;
# OceanBase V4.x 版本检查日志是否同步，返回为空说明已同步
select count(1) as unsync_cnt from GV$OB_LOG_STAT where in_sync = 'NO';