This tip can help clear some confusion when you encounter the following error while forcing replication:

result 8461 The replication operation was preempted

Here is the output of running repadmin /showreps on a brand new domain controller:

DC=contoso,DC=com
    5th_Ward\ContosoDC2 via RPC
    objectGuid: 5ed02b33-a6ab-4576-b109-bb688221e6e3       

Last attempt @ 2008-08-21 17:51.44 failed, result 8461:   The replication operation was preempted.
Last success @ (never).

If you use the verbose switch you will see the following:

DC invocationID:
5ed02b33-a6ab-4576-b109-bb688221e6e3 DO_SCHEDULED_SYNCS WRITEABLE
COMPRESS_CHANGES NO_CHANGE_NOTIFICATIONS NEVER_SYNCED PREEMPTED USNs:
577738/OU, 0/PU Last attempt @ 2008-08-21 17:51:44 was delayed for a
normal reason, result 8461 (0x210d): The replication operation was preempted.
Last success @ (never).

The reason we log this message is because there is an ongoing higher priority replication operation that has not completed yet.  In order to see what inbound replication items are queued (and have preempted us) run the following command on the dc:

repadmin /queue

If you have a lot of items queued run:

repadmin /queue >c:\repl_queue.txt

This will output a list of inbound replication tasks that are queued.  They are listed by task id in order of priority.  The replication operation that we are waiting on is at the top of the list.

If you want to find out what objects/attributes are currently being replicated in to this dc we can enable diagnostic logging for "5 Replication Events" (coming in a future post)  However, Steve Patrick(Spat) shows us a cool repadmin cmd in his post here.

repadmin /showchanges ContosoDC2 5ed02b33-a6ab-4576-b109-bb688221e6e3 DC=corp,DC=com >changes.txt

Part 2 of this post will come at a later date.  Stay tuned...