Just wanna know how mcid works in adobe data feed. And, When I check my feeds, in the exported csv file, I have some mcid's missing for some users mcid has been duplicated multiple times. I wanna know the reason for this. Please, reply me at the earliest.
If you are referring to data feed column mcvisid which is Experience Cloud Visitor ID, then it is an 128-bit number consisting of two concatenated 64-bit numbers padded to 19 digits.
This column does not contain value of query parameter mid from the server call as it is. In case some mcvisid values are missing, most likely the server call did not fire or was not successful. This value remains same for a unique visitor using same browser unless cookies are cleared hence, there could be multiple rows with the same mcvisid value depicting multiple hits/visits from the same visitor.