Understanding InnoDB Tablespace Duplicate Check (MySQL Startup with Many Tables)

This post is a little long, please bear with me as after the intro, you can skip to the essential.

In the last weeks / months, I have been working on understanding / improving MySQL startup with many tables.  I already wrote three posts on the subject, they are listed below.  In this post, I focus on describing the startup phase InnoDB Tablespace Duplicate Check (Duplicate Check for short).  This allows to better understand the optimization I already submitted, and find another optimization that could be leveraged.

Long and Silent / Stressful MySQL Startup with Many Tables

In the last weeks / months, I have been working on understanding / improving MySQL startup with many tables.  I already wrote two posts on the subject, the links are below.  So far, I did not share what brought my attention to this, and it is the subject of this post.  Also, and because it is related, I come back to the optimization / contribution I already made on the subject, looking at it with new information from this post.