Connection management through the Connection Manager
Connection Managers can control automatic failover for high-availability clusters, monitor client connections and direct requests to appropriate database servers, act as proxy servers and handle client/server communication, and prioritize connections between application servers and the primary server of a high-availability cluster. Connection Managers support high-availability clusters, replicate sets, server sets, and grids.
Automatic failover for database servers
If the Connection Manager detects that a primary server of a high-availability cluster has failed, it can promote a secondary server to the role of the primary server.
If you use multiple Connection Managers
to manager failover for a cluster, you can enforce a consistent failover
policy by setting the onconfig file HA_FOC_ORDER
configuration parameter on the cluster's primary server. The value
of the onconfig file HA_FOC_ORDER configuration
parameter replaces the value of the FOC parameter's ORDER attribute
in the configuration file of each Connection Manager that connects
to the primary server.
Rule-based connection redirection and load balancing
Client applications can connect to a Connection Manager as if they are connecting to a database server. The Connection Manager gathers workload statistics from each server in the connection unit and uses service level agreements (SLAs) to manage and direct client connection requests to appropriate servers. When a client application makes a connection request through a redirect-mode SLA, the Connection Manager returns a database server's IP address and port number to the client application. The client application then uses the information to connect to the specified database server.
Connection Manager redirection takes place in the communication layer, so additional action is not required by client applications. Connection Managers can use redirection policies that are based on workload, latency, apply failures, or the apply backlog. Redirection can also be configured to occur round-robin.
Redirection-policy SLAs do not support connections from application that are compiled with Data Server Driver for JDBC and SQLJ version 3.5.1 or before, or with HCL OneDB™ Client Software Development Kit (Client SDK) 3.00 or before.
Proxy-server connection management
Proxy-mode SLAs and redirect-mode SLAs are similar; in both cases, the Connection Manager gathers workload statistics from connection-unit servers, and controls which servers receive client connection request servers. When a client application makes a connection request through a proxy-mode SLA, client/server communication travels through the Connection Manager. When a database server is behind a firewall, Connection Managers can act as proxy servers, and handle client/server communication.
Proxy-policy SLAs do not have the same version restrictions that redirect-policy SLAs have. Connections from application that are compiled with any version of Data Server Driver for JDBC and SQLJ, or with any version of HCL OneDB Client Software Development Kit (Client SDK) are supported.
Failover prioritization for application servers
You can install Connection Managers on the same hosts as application servers, and then prioritize the connections between each application server and the primary server of a high-availability cluster. This can help the highest priority application server maintain a connection to the cluster's primary server if a portion of the network fails.