siyum - Tachanun when there is a Siyyum?

1. 
   

   Does a minyan say tachanun if there was a siyyum or if there is going to be after aleinu? Or, is it preferable to have a Siyum on Shabbat (just for example) to avoid this safeik?

   
   


2. 
   
   

   Is Tachanun recited at a Siyum of all the Masechtot of Sha"S Bavli?

   
   

http://en.wikipedia.org/wiki/Siyum