Query Throttling issue after increasing List view threshold in connected webpart

Dear SharePointers,

                               I have connnected listview webpart deployed on site. Parent webpart has 16 fields and over 3,000 listitems exists in list. Child webpart has 7 fields and more than 30,000 Items. The code works well in other sites in same web app and it also works well in other systems. We tested same in other system by increasing/decreasing data but still we are not able to replicate issue. I know that this issue could also encounter if fields are not indexed in the list. Are there any other pointers which can use to debug this issue.

Milan Chauhan