The default Data Replicator configuration allows each Replicator Service to establish up to 100 simultaneous connections to its control database. You can change the connection limits via the ControlDB tab of the Service Properties dialog.
When the Replicator Manager connects to the Service and its associated control database, two connections are reserved for use by the Replicator Manager session. These connections are not counted toward the total number of connections governed by the Maximum Number of Connections setting.
To identify reserved connections, select the Connections folder in the left pane of the Replicator Manager main window, and then select the Details command from the View menu. The connection that is reserved for the Replicator Service to communicate with its control database has a name of ControlDB in the Type column of the right pane.
If the number of currently active connections is greater than or equal to the value for Maximum Number of Connections, you cannot establish a new connection or obtain access to a previously pooled connection. If you start an operation that requires such a connection, Replicator Manager may enter a waiting state until a connection is available or a specific timeout period has passed. Similarly, replication operations may fail, showing error messages such as "Could not add connection to list." If an operation fails in this manner, the Data Replicator attempts to re-run the subscription at its next scheduled replication time. To avoid replication failures due to connection limits, increase Maximum Number of Connections to a higher value, decrease the group concurrency settings, or change the replication schedules to reduce the number of subscriptions that run simultaneously.
To stop incremental subscriptions from communicating with a host, such as when the host needs to be taken offline for maintenance, pause the subscriptions that use the host and then delete the connections that are established to it. When the host is again available you can resume the subscriptions, which re-establishes the connections.