Partial connectivity means two or more cache servers are connected with each other but not fully connected. It could be that the active partition on one cache server is no longer connected to its replica on another cache server even though the active partition on that other server is connected to its replica on the original server. Or, it could be that one of the cache servers is totally disconnected with other servers in the cluster.
Additionally, in Partition Replica Cache, each cache server contains one active partition and one replica partition. The replica is passive and only accessed by its active partition. But, at cache cluster layer, both active partition and the replica are seen as independent "nodes". So, a 3 server cache cluster in Partition-Replica Cache will have a "6 node" cluster.
Use View Cluster Connectivity tab in NCache Manager
In the example below, it shows a fully connected (healthy) cache cluster. There are 3 servers in the cluster and 6 "nodes". So, each "node" is supposed to be connected to 5 other "nodes" as shown in "Connected to Nodes" column.
Node Address | Connected to Nodes | Status |
20.200.20.100 |
20.200.20.100, 20.200.20.101, 20.200.20.101, 20.200.20.102, 20.200.20.102 |
Fully Connected |
20.200.20.101 |
20.200.20.101, 20.200.20.100, 20.200.20.100, 20.200.20.102, 20.200.20.102 |
Fully Connected |
20.200.20.102 |
20.200.20.102, 20.200.20.100, 20.200.20.100, 20.200.20.101, 20.200.20.101 |
Fully Connected |
In the example below, it is a partially connected cache cluster where 20.200.20.101 has lost connectivity with its replica on 20.200.20.102 and is missing a connection to 20.200.20.102 node. Hence, it has less number of nodes shown in "Connected to Columns" in front of it.
Node Address | Connected to Nodes | Status |
20.200.20.100 |
20.200.20.100, 20.200.20.101, 20.200.20.101, 20.200.20.102, 20.200.20.102 |
Partially Connected |
20.200.20.101 |
20.200.20.101, 20.200.20.100, 20.200.20.100, 20.200.20.102 |
Partially Connected |
20.200.20.102 |
20.200.20.102, 20.200.20.100, 20.200.20.100, 20.200.20.101, 20.200.20.101 |
Partially Connected |
In the example below, this is another partially connected cache with a Split Brain, where 20.200.20.102 has lost connectivity completely to other two nodes and hence showing Single Node cache Cluster status. Also, 20.200.20.100 and 20.200.20.101 are showing partially connected status and are missing 20.200.20.102 in the "connected to Nodes" column.
Node Address | Connected to Nodes | Status |
20.200.20.100 | 20.200.20.100, 20.200.20.101, 20.200.20.101 | Partially Connected |
20.200.20.101 | 20.200.20.101, 20.200.20.100, 20.200.20.100 | Partially Connected |
20.200.20.102 | --- | Single Node cache Cluster |
You have to start one or more cache servers to fix partial connectivity. In a 2-server cluster, you only need to start one of the cache servers. In case of a 3-server cluster, you may have to restart 2 cache servers.
OR
AND/OR
AND/OR
Once a cache cluster is in partially connected state then it requires manual intervention to recover. Here are the steps to resolve this problem,
C:\Program Files\NCache\bin\tools>stopcache CacheName /s 20.200.20.102
C:\Program Files\NCache\bin\tools>startcache CacheName /s 20.200.20.102