A logical server allows one or more servers of a multiplex to be grouped together to serve one or more applications or users.
When you connect to a logical server and run a query, SAP Sybase IQ distributes the query execution to only those nodes that are members of the logical server. You can dynamically add or drop member nodes for a logical server to accommodate the changing resource needs of applications.
Access to SAP Sybase IQ multiplex nodes is provided only via logical servers. You can create multiple logical servers to serve different groups of applications or users. When you create a logical server, explicitly select one or more multiplex servers to add them as members. A multiplex node can be a member of more than one logical server. A logical server can have both reader and writer nodes. You can also make the coordinator node a member of a logical server, although specific rules govern coordinator membership.
A workload directed to a logical server can only be processed by member servers. Only queries that can be parallelized are eligible for work distribution; all other operations are confined to the node of initial connection. Users must connect to a node that has the role (reader or writer) required for the intended operation.