In the copy_set function in the slon remote_worker when we copy the set 
from the origin we construct values for the initial snapshot (for 
sl_setsync) by the following method

* Get the max SYNC event on the origin and snapshot information for that 
sync
* Query all sl_log_1 and sl_log_2 entires that came in after that sync. 
This information populates the action list.

Why don't we just get the snapshot visibility information of what is and 
isn't visible to the copy_set transaction directly with 
txid_current_snapshot() ?

It seems simpler?   (I would guess that this is a left-over from the 
pre-8.3 days when txid_current_snapshot wasn't available?)

I ask because the current method work with logical replication because 
sl_log will be empty (but we still need the snapshot of the copy_set to 
filter stuff out later).   I'd like to modify copy_set to just use 
txid_current_snapshot for both logical and trigger based cases.

If there some reason why this won't work then please let me know.

Thanks