visid_high / low vs MCVISID

[klj43va]

Hi all, it seems this question has been asked a few time but none of the previous questions have been answered so I wanted to try and get to the bottom of this.

We moved to the ECID service about 5 years ago and have data feeds set to export the data to AWS / GCP.  We have multiple sites / apps and also performed the single domain migration in Adobe so we could use the first party cookies across all of our architecture. 

Now the documentation states that visid_high / low are set by the MID which is read from the s_vi cookie and that concatenating them would give you a unique visitor ID, however other documentation states that the ECID is the most accurate way of identifying a customer which is stored as MCVISID in the data feeds.  

To also set some further context all of the visitors I am analysing have been Identified by the ECID service & also have visid_high / low set as well.

My question is as follows:

A) Have I understood this correctly or am I barking up the wrong tree.

B) If I have why is s_vi being used when ECID is better 

C) Which is the best ID to use for tracking visitors across our digital estate

D) Why do some ECID have more than one concat visid & vice versa 

Really appreciate any help with this as I'm currently banging my head against a wall

[Jennifer_Dungan · Accepted solution]

There are a lot of mysteries around all the Adobe ids.. so I understand your frustrations.

For what it's worth, we have visid high/low for all our users as well, and we have been on ECID for years too.

From what I have been able to glean...

Way way with s_vi, those cookies would be set per domain.. sometimes I still get those cookies set today... each domain would have a separate s_vi value....

ECID however tries to identify the same user hitting any of your domains, and set the same id for all your sites.. this is why it's better.. it allows you to fingerprint users across domains and suites.  It also does its best to reset the same value for the user if it gets deleted (sometimes this is impossible, but it's better than visid which doesn't even attempt to do such a thing, it just creates a new id)

Because ECID is an "organization ID" and should be shared by multiple properties, I would say it's the better choice.

One ECID having multiple visid is likely due to what I said above... ECID tries to keep the same user with the same ID, and attempts to re-set the same id back to the user if it gets lost... so the ECID may get set properly, but the visid would create a new id and use that until its lost again.

The other way around.. Do you have a mobile app / are you using the appendVisitorIDsTo function? This allows you to take the ECID (usually from an app, but sometimes from another domain) and append it to the URL.. then the site you land on will discard it's ECID in favour of the appended version.

So if you are on a Mobile App (which is treated like a separate browser / device within the tracking infrastructure) you can at least do a one way user stitch between the app and your website... or if your different domains somehow fingerprinted the user with separate ECIDs, it will start to force a single ECID to them...