All this is prety straight forward.
As for the transaction you are crating, is the process of 'split
message' actually do on the DB side or are you doing this process on
you side? Maybe this is the actual work of splitting the message by
the DB that is very slow.
/Maybe/ if you do this data-processing on your side, then sending that
to the DB will save you time. If you really want that job being done
on the server side, you could build yourself an extension module
adding a special function that you would call to do the job. Maybe you
could win couple cycles...
But all that could be confirmed or not by someone else which knows
more about PG internals.
Best regards.
--
Alexandre Leclerc