Impaction odd shaped poo, partial impation?

My boar Pudding is about 2 years old and seems to be pooing regularly but some times the poos have a groove along one side (looks like a pit from a date) I was wondering if this is from squeezing past a partial impaction but when I tried to check his sack all I could see was a bit of hay which seemed too soft to cause the groove.

Is this normal?