openGauss 主备切换之 switchover 与 failover
switchover
在主备机正常时，出于维护的需要，将备机切换为主机，可保证切换过程中数据不丢失。
查看集群实例主备状态：1 节点为主库，2 节点为备库。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Normal
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Primary Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Standby Normal
在备节点执行切换主备操作：
$ gs_ctl switchover -D /opt/openGauss/data/dn
[2021-01-15 02:44:55.125][1034][][gs_ctl]: gs_ctl switchover ,datadir is /opt/openGauss/data/dn
[2021-01-15 02:44:55.125][1034][][gs_ctl]: switchover term (1)
[2021-01-15 02:44:55.137][1034][][gs_ctl]: waiting for server to switchover..............
[2021-01-15 02:45:06.250][1034][][gs_ctl]: done
[2021-01-15 02:45:06.250][1034][][gs_ctl]: switchover completed (/opt/openGauss/data/dn)
确认集群主备状态：1 节点为备库，2 节点为主库。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Normal
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Standby Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Primary Normal
保存数据库主备机器信息：确保 gs_om -t refreshconf 命令执行成功，否则再次重启会影响数据库状态。
$ gs_om -t refreshconf
Generating dynamic configuration file for all nodes.
Successfully generated dynamic configuration file.
failover
在主机异常时，将备机切换为主机。
查看集群实例主备状态：1 节点为备库，2 节点为主库。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Normal
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Standby Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Primary Normal
备节点执行主备切换操作：
$ gs_ctl failover -D /opt/openGauss/data/dn
[2021-01-15 03:33:13.803][17292][][gs_ctl]: gs_ctl failover ,datadir is /opt/openGauss/data/dn
[2021-01-15 03:33:13.803][17292][][gs_ctl]: failover term (1)
[2021-01-15 03:33:13.810][17292][][gs_ctl]: waiting for server to failover...
[2021-01-15 03:33:14.823][17292][][gs_ctl]: done
[2021-01-15 03:33:14.823][17292][][gs_ctl]: failover completed (/opt/openGauss/data/dn)
确认集群主备状态：双主状态。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Unavailable
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Primary Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Primary Normal
在确定降为备机的节点关闭并以 standy 模式启动 openGauss 服务：
$ gs_ctl start -D /opt/openGauss/data/dn -M standby
[2021-01-15 03:03:08.695][9126][][gs_ctl]: gs_ctl started,datadir is /opt/openGauss/data/dn
[2021-01-15 03:03:08.864][9126][][gs_ctl]: waiting for server to start...
......
[2021-01-15 03:03:10.921][9126][][gs_ctl]: done
[2021-01-15 03:03:10.921][9126][][gs_ctl]: server started (/opt/openGauss/data/dn)
确认集群状态：1 节点为主库，2 节点为备库，但备库需要修复。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Degraded
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Primary Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Standby Need repair(WAL)
在备库所在节点执行修复命令：
[omm@cen7-og1-03 ~]$ gs_ctl build -D /opt/openGauss/data/dn
[2021-01-15 03:23:57.702][30784][][gs_ctl]: gs_ctl incremental build ,datadir is /opt/openGauss/data/dn
waiting for server to shut down.... done
server stopped
[2021-01-15 03:23:58.726][30784][][gs_ctl]: fopen build pid file "/opt/openGauss/data/dn/gs_build.pid" success
[2021-01-15 03:23:58.726][30784][][gs_ctl]: fprintf build pid file "/opt/openGauss/data/dn/gs_build.pid" success
[2021-01-15 03:23:58.727][30784][][gs_ctl]: fsync build pid file "/opt/openGauss/data/dn/gs_build.pid" success
......
[2021-01-15 03:24:02.833][30784][dn_6001_6002][gs_ctl]: done
[2021-01-15 03:24:02.833][30784][dn_6001_6002][gs_ctl]: server started (/opt/openGauss/data/dn)
[2021-01-15 03:24:02.833][30784][dn_6001_6002][gs_ctl]: fopen build pid file "/opt/openGauss/data/dn/gs_build.pid" success
[2021-01-15 03:24:02.833][30784][dn_6001_6002][gs_ctl]: fprintf build pid file "/opt/openGauss/data/dn/gs_build.pid" success
[2021-01-15 03:24:02.835][30784][dn_6001_6002][gs_ctl]: fsync build pid file "/opt/openGauss/data/dn/gs_build.pid" success
确认集群状态：正常。
$ gs_om -t status --detail
[ Cluster State ]
cluster_state : Normal
redistributing : No
current_az : AZ_ALL
[ Datanode State ]
node node_ip instance state | node node_ip instance state
1 cen7-og1-02 ... 6001 /opt/openGauss/data/dn P Primary Normal | 2 cen7-og1-03 ... 6002 /opt/openGauss/data/dn S Standby Normal
保存数据库主备机器信息：确保 gs_om -t refreshconf 命令执行成功，否则再次重启会影响数据库状态。
$ gs_om -t refreshconf
Generating dynamic configuration file for all nodes.
Successfully generated dynamic configuration file.