数据库版本：
test=# select version();
version
----------------------------------------------------------------------------------------------------------------------
KingbaseES V008R006C005B0041 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
(1 row)
主机节点信息：
[kingbase@node101 bin]$ cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.1.101 node101 ， #主库
192.168.1.102 node102 #备库
集群节点信息：
ID | Name | Role | Status | Upstream | repmgrd | PID | Paused? | Upstream last seen
----+---------+---------+-----------+----------+---------+-------+---------+--------------------
1 | node101 | primary | * running | | running | 11180 | no | n/a
2 | node102 | standby | running | node101 | running | 9242 | no | 0 second(s) ago
一、查看集群状态及配置信息
1、集群节点状态
[kingbase@node101 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+-----------+----------+----------+----------+----------+----------------------------------------------------------------------------------------------------------------------------------------------------
1 | node101 | primary | * running | | default | 100 | 1 | host=192.168.1.101 user=system dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
2 | node102 | standby | running | node101 | default | 100 | 1 | host=192.168.1.102 user=system dbname=esrep port=54321 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
2、集群配置信息
1、备库网卡down
[root@node102 ~]# ifconfig enp0s3 down
2、查看备库messages日志
3、备库hamgr.log
=日志信息显示repmgrd服务被close，无法提供正常的服务。=
4、主库查看集群节点状态
[kingbase@node101 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+---------------+----------+----------+----------+----------+------------------------------------------------------------------------------------------------------------------------------------------------
1 | node101 | primary | * running | | default | 100 | 1 | host=192.168.1.101 user=system dbname=esrep port=5 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
2 | node102 | standby | ? unreachable | node101 | default | 100 | ? | host=192.168.1.102 user=system dbname=esrep port=5 connect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
WARNING: following issues were detected
- unable to connect to node "node102" (ID: 2)
- node "node102" (ID: 2) is registered as an active standby but is unreachable
=== 从以上信息所示，集群没有触发主备库的切换操作。===
三、备库网卡恢复正常（up）
1、查看集群状态信息
[kingbase@node101 bin]$ ./repmgr cluster show
ID | Name | Role | Status | Upstream | Location | Priority | Timeline | Connection string
----+---------+---------+-----------+----------+----------+----------+----------+------------------------------------------------------------------------------------------------------------------------------------------------
1 | node101 | primary | * running | | default | 100 | 1 | host=192.168.1.101 user=system dbname=esrep port=54321nect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
2 | node102 | standby | running | node101 | default | 100 | 1 | host=192.168.1.102 user=system dbname=esrep port=54321nect_timeout=10 keepalives=1 keepalives_idle=10 keepalives_interval=1 keepalives_count=3
2、查看备库hamgr.log
=如下日志所示，备库网卡恢复正常后，备库通过接收wal日志流执行recovery，和主库同步。=
[2022-03-29 16:11:45] [INFO] node "node102" (ID: 2) monitoring upstream node "node101" (ID: 1) in normal state
[2022-03-29 16:11:45] [ERROR] unable to determine if server is in recovery
[2022-03-29 16:11:45] [DETAIL]
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
[2022-03-29 16:11:45] [DETAIL] query text is:
SELECT pg_catalog.pg_is_in_recovery()
[2022-03-29 16:11:47] [NOTICE] upstream is available but upstream connection has gone away, resetting
[2022-03-29 16:12:24] [ERROR] is_rep_sync_streaming(): get 2 tuples
[2022-03-29 16:12:45] [ERROR] is_wal_all_recevied(): get 0 tuples
[2022-03-29 16:12:45] [ERROR] is_rep_sync_streaming(): get 0 tuples
[2022-03-29 16:12:47] [ERROR] is_wal_all_recevied(): get 0 tuples
[2022-03-29 16:12:47] [ERROR] is_rep_sync_streaming(): get 0 tuples
[2022-03-29 16:12:49] [ERROR] is_wal_all_recevied(): get 0 tuples
[2022-03-29 16:12:49] [ERROR] is_rep_sync_streaming(): get 0 tuples
[2022-03-29 16:16:47] [INFO] node "node102" (ID: 2) monitoring upstream node "node101" (ID: 1) in normal state
四、总结
1、对于备库，如果网卡down引起的网络故障，并不会触发集群的主备切换。当网卡正常后，集群恢复正常。
2、如果备库的数据库服务down，在recovery=‘automatic | standby’配置时，会自动恢复备库的数据库服务。
3、本案例是在一主一备的架构下的测试，如果是一主多备的架构，对于同步状态是‘sync’的备库网卡down，会导致其他的备库进行竞选，将同步状态提升为‘sync’。
