R: [GENERAL] Postgres 9.6.1 big slowdown by upgrading 8.4.22

Hi guys,

Here is an update, i think i have found the right statement that bring Postgresql 9.6.1 under heavy-use of resources
(CPU)in a massive benchmark. 

I only try to remove one simple, but very simple, condition:

and (grulist.stato is null or grulist.stato!=2)

Grulist.stato field is numeric and has a btree index on it.

Very strange: if i leave only one condition (example: grulist.stato is null) no heavy-cpu use occurred (but i need the
twoconditions with the OR). 
But when combyning the two conditions (grulist.stato is null OR grulist.stato != 2) something happens...

The single explain analyze is very fast and maybe there is something that create a strange condition for postgresql
9.6.1that takes CPU resources. 

The btree index is right for this (numeric) two conditions?

Thank you again!
/F