There are two ways to use -s to synchronize multiple subscriptions:
Specify -s sub1,sub2,sub3 to synchronize sub1, sub2, and sub3 in one upload followed by one download.
In this case, if you have set extended options on the subscriptions, only the options set on the first subscription in the
list are used. Extended options set on subsequent subscriptions ignored.
Specify -s sub1 -s sub2 -s sub3 to synchronize sub1, sub2, and sub3 in three separate sequential synchronizations, each with its own upload and download.
When successive synchronizations occur very quickly, such as when you specify -s sub1 -s sub2, dbmlsync could start processing a synchronization when the server is still processing the previous synchronization. In this
case, the second synchronization fails with an error indicating that concurrent synchronizations are not allowed. If you run
into this situation, you can define an sp_hook_dbmlsync_delay stored procedure to create a delay before each synchronization.
Usually a few seconds to a minute is a sufficient delay.