To help people understand what this slightly complex module actually does I made some sequence diagrams.
There is one for Apache Solr and one for what Acquia Search does to extend it.
These resources are also available on drupal.org :
Apache Solr Sequence Diagram
Acquia Search Sequence Diagram
Have fun!
About Nick Veenhof
I have been involved in open source communities for almost 15 years now, with the majority of that in the Drupal ecosystem, but have interacted with a lot more technologies. I'm no stranger to cloud infrastructure and the devops iterative way-of-working. Aside from technology, I try to be a good coach & mentor by embracing change and to lead by example. Next to this,I am advocating Open Source. At Gitlab I'm working on how to make it easier and more rewarding to contribute to GitLab and try to make our digital world a better and more open place compared to yesterday.