You can realize significant performance improvement by grouping subscriptions that perform snapshot replication. Subscriptions that perform incremental replication must belong to a group.
Grouping subscriptions provides for high speed replication because they can be run concurrently to take advantage of multi-threading. With multi-threading the Data Replicator can continue fetching data even if another subscription in the group is idle while it waits for an operation to complete.
Groups provide a way to organize existing subscriptions so you can run all the replication operations at once. If the subscriptions in the group are dependent on one another, such that each should not run until the prior subscription completes, you can set the group concurrency level to 1 so they run one at a time. If you want all of the subscriptions in the group to complete as quickly as possible, increase the group concurrency setting to take advantage of multi-threading the operations. See Controlling the Run Order of Subscriptions for more information about the order in which subscriptions run within a group.
Each subscription remains associated with the source under which it is defined, but snapshot subscriptions can be referenced from one or more groups. A subscription that performs incremental replication can belong to only one group, and all the subscriptions in the group must use the same source and destination.
There are two ways to create a group: 1) you can create a group and then add subscriptions to it, or 2) you can create a new group as you are using the Add Subscription Wizard to define subscriptions. After a group is created you can add one or more subscriptions to it either as you are defining a new subscription or by selecting the group and adding an existing subscription to it.
Use the Insert Group command or the Insert Incremental Group command to create a group so you can then add existing subscriptions as members.
Select the Groups folder, right-click, and select the Insert Group or Insert Incremental Group command, as appropriate. (SQDR Plus is required to define a group that performs incremental replication.)
Specify the General group properties, naming the group and choosing whether to replicate indexes and/or constraints and the desired level of error recovery and concurrency.
For a group of snapshot subscriptions, click the Member Subscriptions tab. From the Available Subscriptions pane select the subscriptions you want to add to the group and click the > arrow button, or click the >> button to add all the available subscriptions to this group.
For a group of incremental subscriptions, click the Advanced tab and select the source and destination you want to use. After the group is created, select the Members folder, right-click, and execute the Insert Member command. The Add Subscription Wizard appears so you can select the specific object(s) to replicate from the source defined for this group.