Replication lets you enable warnings for several conditions. This includes exceeding a specified length of time for synchronizing changes between a merge Publisher and Subscriber. Different times can be specified for LAN connections and dial-up connections.
When you enable a warning by using Replication Monitor or sp_replmonitorchangepublicationthreshold, you specify a threshold that determines when a warning is triggered. When that threshold is met or exceeded, a warning is displayed in Replication Monitor, and an event is written to the Windows event log. Reaching a threshold can also trigger a SQL Server Agent alert. For more information, see Set Thresholds and Warnings in Replication Monitor and Programmatically Monitor Replication.
If a subscription exceeds a duration threshold, you must determine whether there is a performance issue with the system or whether the threshold should be adjusted. After you configure replication, develop a performance baseline that will let you determine how replication behaves with a workload that is typical for your applications and topology. Include duration of synchronization in this baseline so that you can set an appropriate value for the threshold.
If the threshold value is appropriate, but it is being exceeded, you must determine where the performance bottleneck is in the system. For more information about how to monitor and troubleshoot replication performance, see the following topics:
Monitor Performance with Replication Monitor (especially the section "Viewing Detailed Synchronization Performance for Merge Replication")