Is it OK to have two "_ga" cookies in universal analytics, one for domain and one for subdomain

Question

Our website has a number of sub-domains and we are in the process of migrating from classical analytics to universal analytics. When we migrated one of our domain from classical to universal analytics, with google tag manager, it started creating two _ga cookies. One against our main domain and another against the subdomain which looked like following -

cookie 1 - _ga - GA1.2.9876543210.9876543210 - .mysite.com
cookie 2 - _ga - GA1.3.9876543210.9876543210 - .subdomain.mysite.com

Now I understand that GA1.2 stands for main domain cookie and GA1.3 stands for subdomain cookie. But I could not find answers of my following two queries -

1. Will this multiple cookie system create any problem in my data?
2. Is there any analytical use of creating two cookies?

I tried to search in google and forums regarding multiple "_ga" cookies but could not find any reference.

I also tried to see other sites using UA but could not see any site which creates separate cookies for domain and subdomain.

Answer 1

This is not completly correct and you probably facing the problem with sef-referrals in your analytics (I have it too). In GTM you need to go to 'fields to set' en set the cookieDomain to auto. If you do cross-domain tracking as well, you need to set allowLinker to true and add the domains under cross-domain tracking field of you GA Universal Tag.

Answer 2

this issue was raised long time ago but seems that it's still alive, as I have encountered the same :)

I would like to refer you an article that covers this issue rigorously: https://www.simoahava.com/analytics/cookie-settings-and-subdomain-tracking-in-universal-analytics/

You might need to include cookieDomain:auto for the Universal Analytics pageview tag.