案例说明：
在一主多备的架构中，需要配置一台备库在主备切换时，不能选举为主库。对于repmgr主备切换主库的选择算法如下：
Tips：
Repmgr选举候选备节点会以以下顺序选举：LSN ---->Priority----> Node_ID。
系统会先选举一个LSN比较大者作为候选备节点；如LSN一样，会根据Priority优先级进行比较，该优先级是在配置文件中进行参数配置；如优先级也一样，会比较节点的Node ID，小者会优先选举。在选举主机过程中，权重高的备机具有升主的更高优先级，如果权重为0，则该备机永远不会升级为主机。
repmgr集群，默认主备库优先级都是100：
对于repmgr.conf中的参数priority：
priority=60
权重，在选举主机过程中，权重高的备机具有升主的更高优先级，如果权重为0，则该备机永远不会升级为主机
修改priority参数：
适用版本：
KingbaseES V8R6
测试案例：
1、切换前集群节点状态
[kingbase@node1 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+-----------+----------+----------+----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------
1 | node248 | primary | * running | | default | 100 | 10 | host=192.168.7.248 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
3 | node243 | standby | running | node248 | default | 0 | 10 | host=192.168.7.243 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
** 2、修改repmgr.conf中priority参数**
[kingbase@node1 etc]$ vi repmgr.conf
on_bmj=off
.......
priority=0
重新注册备库：
[kingbase@node3 bin]$ ./repmgr standby register --force
INFO: connecting to local node "node243" (ID: 3)
INFO: connecting to primary database
INFO: standby registration complete
NOTICE: standby node "node243" (ID: 3) successfully registered
在集群节点状态信息中，standby的priority显示为0：
3、重启主库系统做failover切换测试
[root@node1 ~]#reboot
4、在备库查看集群节点状态
=== 如下所示，集群未发生切换,只是显示主库不能连接===
[kingbase@node3 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+---------------+-----------+----------+----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------
1 | node248 | primary | ? unreachable | | default | 100 | ? | host=192.168.7.248 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
3 | node243 | standby | running | ? node248 | default | 0 | 10 | host=192.168.7.243 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
WARNING: following issues were detected
- unable to connect to node "node248" (ID: 1)
- node "node248" (ID: 1) is registered as an active primary but is unreachable
- unable to connect to node "node243" (ID: 3)'s upstream node "node248" (ID: 1)
- unable to determine if node "node243" (ID: 3) is attached to its upstream node "node248" (ID: 1)
5、主库系统重启后，启动数据库服务
[kingbase@node1 bin]$ ./sys_ctl start -D ../data
waiting for server to start....2021-03-01 12:03:41.870 CST [5257] LOG: sepapower extension initialized
2021-03-01 12:03:41.893 CST [5257] LOG: starting KingbaseES V008R006C003B0010 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
2021-03-01 12:03:41.893 CST [5257] LOG: listening on IPv4 address "0.0.0.0", port 54321
2021-03-01 12:03:41.893 CST [5257] LOG: listening on IPv6 address "::", port 54321
2021-03-01 12:03:42.030 CST [5257] LOG: listening on Unix socket "/tmp/.s.KINGBASE.54321"
2021-03-01 12:03:42.454 CST [5257] LOG: redirecting log output to logging collector process
2021-03-01 12:03:42.454 CST [5257] HINT: Future log output will appear in directory "sys_log".
. done
server started
6、集群节点状态恢复正常
[kingbase@node1 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+-----------+----------+----------+----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------
1 | node248 | primary | * running | | default | 100 | 10 | host=192.168.7.248 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
3 | node243 | standby | running | node248 | default | 0 | 10 | host=192.168.7.243 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
7、查看备库repmgr.log日志
=== 提示备库priority=0 ，不能提升为主库===
[2021-03-01 12:43:30] [NOTICE] starting monitoring of node "node243" (ID: 3)
[2021-03-01 12:43:30] [INFO] "connection_check_type" set to "ping"
[2021-03-01 12:43:30] [INFO] monitoring connection to upstream node "node248" (ID: 1)
[2021-03-01 12:43:30] [NOTICE] wal catched_up state changed to 1
[2021-03-01 12:45:00] [WARNING] unable to ping "host=192.168.7.248 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3"
[2021-03-01 12:45:00] [DETAIL] PQping() returned "PQPING_REJECT"
[2021-03-01 12:45:00] [WARNING] unable to connect to upstream node "node248" (ID: 1)
[2021-03-01 12:45:00] [INFO] sleeping 5 seconds until next reconnection attempt
[2021-03-01 12:45:05] [INFO] checking state of node 1, 1 of 3 attempts
[2021-03-01 12:45:15] [WARNING] unable to ping "user=esrep connect_timeout=10 dbname=esrep host=192.168.7.248 port=54321 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3 fallback_application_name=repmgr"
[2021-03-01 12:45:15] [DETAIL] PQping() returned "PQPING_NO_RESPONSE"
[2021-03-01 12:45:15] [INFO] sleeping 5 seconds until next reconnection attempt
[2021-03-01 12:45:20] [INFO] checking state of node 1, 2 of 3 attempts
[2021-03-01 12:45:30] [WARNING] unable to ping "user=esrep connect_timeout=10 dbname=esrep host=192.168.7.248 port=54321 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3 fallback_application_name=repmgr"
[2021-03-01 12:45:30] [DETAIL] PQping() returned "PQPING_NO_RESPONSE"
[2021-03-01 12:45:30] [INFO] sleeping 5 seconds until next reconnection attempt
[2021-03-01 12:45:35] [INFO] checking state of node 1, 3 of 3 attempts
[2021-03-01 12:45:45] [WARNING] unable to ping "user=esrep connect_timeout=10 dbname=esrep host=192.168.7.248 port=54321 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3 fallback_application_name=repmgr"
[2021-03-01 12:45:45] [DETAIL] PQping() returned "PQPING_NO_RESPONSE"
[2021-03-01 12:45:45] [WARNING] unable to reconnect to node 1 after 3 attempts
[2021-03-01 12:45:45] [NOTICE] setting "wal_retrieve_retry_interval" to 86405000 milliseconds
[2021-03-01 12:45:45] [INFO] sleeping 5 seconds
[2021-03-01 12:45:50] [NOTICE] killing WAL receiver with PID 14273
[2021-03-01 12:45:51] [INFO] WAL receiver with pid 14273 killed
[2021-03-01 12:45:52] [NOTICE] WAL receiver disconnected on all sibling nodes
[2021-03-01 12:45:52] [INFO] WAL receiver disconnected on all 0 sibling nodes
[2021-03-01 12:45:52] [NOTICE] this node's priority is 0 so will not be considered as an automatic promotion candidate
[2021-03-01 12:45:52] [NOTICE] setting "wal_retrieve_retry_interval" to 5000 ms
[2021-03-01 12:45:52] [INFO] follower node awaiting notification from a candidate node
8、修改备库优先级为默认优先级
1）注释或删除priority参数配置
2）重新注册standby
[kingbase@node3 bin]$ ./repmgr standby register --force
INFO: connecting to local node "node243" (ID: 3)
INFO: connecting to primary database
INFO: standby registration complete
NOTICE: standby node "node243" (ID: 3) successfully registered
3）查看集群节点状态
[kingbase@node3 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+-----------+----------+----------+----------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------
1 | node248 | primary | * running | | default | 100 | 10 | host=192.168.7.248 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
3 | node243 | standby | running | node248 | default | 100 | 10 | host=192.168.7.243 user=esrep dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
