Is Universal Tracker replacement for Sitecore.Analytics.Tracker or should they be used together?

Question

I am trying to implement simle react app (non JSS) that uses Sitecore headless services. I want to have online personalization, let's say when goal is triggered during current interaction to show the personalized content immediately.

As I experimented with Universal tracker it seems not to possible to achieve this immediate personalization. Since as I understood events from universal tracker are processed in batches with some interval, so they do not appear immediately in xDB. So they could not be used for rules immediately.

So now I am confused with the usage of Universal Tracker and Sitecore.Analytics.Tracker and how they are positioned (what problem solve) in Sitecore in headless scenarios.

So my questions are (in headless context):

1. Is Universal Tracker replacement for Sitecore.Analytics.Tracker in headless scenarios?
2. Or should they be used together but for different scenarios? Like, Sitecore.Analytics.Tracker for online interactions, and Universal tracker for offline interactions.

Answer 1

1. Universal Tracker is first of all a communication channel between xConnect and your none-sitecore application. Yes, it is similar to Sitecore.Analytics.Tracker, but only in context of "it can be used for triggering interactions/events", but it is not a replacement. UT is more like IoT Hub than Sitecore.Analytics.Tracker.
2. Yes. UT can be used for offline interactions but if you don`t have Sitecore context (Sitecore.Analytics.Tracker) or xConnect in your application (desktop, mobile, IoT app). If you can use Sitecore.Analytics.Tracker or xConnect client in your application - use them better.

Also you mentioned that "Since as I understood events from universal tracker are processed in batches with some interval, so they do not appear immediately in xDB".

You can manage this interval: you can change defaults or setup your own channel types/timeouts in "wwwroot\Sitecore.Tracking.Processing.Service\sitecore\Sitecore.Tracking.Processing.ChannelManagement\PipelinesConfig\channelTypes.json"

{
      "Id": "59BD107F-D725-4BA1-91C6-61BEE3CB768C",
      "Name": "UT",
      "IsActive": true,
      "TimeOut": 10,
      "Type": "Sitecore.Tracking.Processing.Abstractions.Channels.Channel, Sitecore.Tracking.Processing.Abstractions"
}

Answer 2

Sitecore.Analytics.Tracker is used only for Sitecore websites . Universal Tracker is used for tracking activities on any website, mobile application, IOT device, Sitecore Websites etc.

In case of headless scenario you can use Sitecore.Analytics.Tracker or Universal tracker.

My advice would be to use Analytics.Tracker as Universal tracker requires additional setup