VMware Cloud Director 维护节点之间的同步流式传输复制。如果备用节点变成未连接状态，则必须确定原因并解决问题。
问题
VMware Cloud Director 设备管理 UI 显示集群运行状况为 DEGRADED，其中一个未连接的备用节点的状态为正在运行，且在备用节点的上游节点名称前面有一个感叹号 (!)。
PostgreSQL 日志显示主节点删除了 WAL 分段。
2020-10-08 04:10:50.064 UTC [13390] LOG: started streaming WAL from primary at 21/80000000 on timeline 17 2020-10-08 04:10:50.064 UTC [13390] FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 000000110000002100000080 has already been removed 2020-10-08 04:10:55.047 UTC [13432] LOG: started streaming WAL from primary at 21/80000000 on timeline 17 2020-10-08 04:10:55.047 UTC [13432] FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 000000110000002100000080 has already been removed
/nodes API 返回以下信息：localClusterHealth 为 DEGRADED，节点的 status 为 running，nodeHealth 为 HEALTHY。在备用节点的上游节点名称前面有一个感叹号 (!)，/nodes API 会返回一条警告，指出备用节点未连接到其上游节点。
例如，
/nodes API 可能会返回以下节点信息。
{
"localClusterFailover": "MANUAL",
"localClusterHealth": "DEGRADED",
"localClusterState": [
{
"connectionString": "host=primary_host_IP user=repmgr dbname=repmgr connect_timeout=2",
"failover": {
"details": "failover = manual",
"mode": "MANUAL",
"repmgrd": {
"details": "On node primary_node_ID (primary_host_name): repmgrd = not applicable",
"status": "NOT APPLICABLE"
}
},
"id": primary_node_ID,
"location": "default",
"name": "primary_host_name",
"nodeHealth": "HEALTHY",
"nodeRole": "PRIMARY",
"role": "primary",
"status": "* running",
"upstream": ""
},
{
"connectionString": "host=unattached_standby_host_IP user=repmgr dbname=repmgr connect_timeout=2",
"failover": {
"details": "failover = manual",
"mode": "MANUAL",
"repmgrd": {
"details": "On node unattached_standby_node_ID (unattached_standby_host_name): repmgrd = not applicable",
"status": "NOT APPLICABLE"
}
},
"id": unattached_standby_node_ID,
"location": "default",
"name": "unattached_standby_host_name",
"nodeHealth": "HEALTHY",
"nodeRole": "STANDBY",
"role": "standby",
"status": "running",
"upstream": "! upstream_host_name"
},
{
"connectionString": "host=running_standby_host_IP user=repmgr dbname=repmgr connect_timeout=2",
"failover": {
"details": "failover = manual",
"mode": "MANUAL",
"repmgrd": {
"details": "On node running_standby_node_ID (running_standby_host_name): repmgrd = not applicable",
"status": "NOT APPLICABLE"
}
},
"id": running_standby_node_ID,
"location": "default",
"name": "running_standby_host_name",
"nodeHealth": "HEALTHY",
"nodeRole": "STANDBY",
"role": "standby",
"status": "running",
"upstream": "upstream_host_name"
}
],
"warnings": [
"node \"unattached_standby_host_name\" (ID: unattached_standby_node_ID) is not attached to its upstream node \"upstream_host_name\" (ID: upstream_node_id)"
]
}
如果备用节点变成未连接状态，则必须尽快重新连接。如果该节点处于未连接状态的时间过长，则在处理来自主节点的连续流式传输的 WAL 记录时可能会落后，并导致无法继续复制。
原因
为确保数据完整性，PostgreSQL 数据库使用预写式日志记录 (WAL)。主节点不断地将 WAL 流式传输到活动备用节点，以便进行复制和恢复。备用节点在接收到 WAL 后对其进行处理。如果备用节点变成未连接状态，则将停止接收 WAL，并且无法作为候选节点提升为新的主节点。
解决方案
- 部署新的备用节点。
- 取消注册未连接的备用节点。
