How does the connection between bugtracker and VCS work?

Question

Version control systems

Good night everyone, my question is this:
I once worked on a project where Trac + Subversion was used . Actually, it is not these softins that are important, but the principle of operation in general.
It looks like this: with each commit, I must indicate the ticket number in the Track, and then when viewing the ticket, I can see a list of all commits to it.
And I'm still very curious about how it works, because as I understand it, Subversion does not use databases, and Trac, on the contrary, pulls all the information from there (unfortunately, I never installed either one or the other).
Thanks in advance to everyone who answers,
Dmitry

Answer 1

Everything is very simple - a post-commit-hook is connected in the main repository, which analyzes the commit log and makes the necessary entries in the Trac / Redmine / etc database

Answer 2

In our redmine, data from SVN is pulled up only when you open the page with the repository browser. Apparently hooks are not configured.
But as I understood from the sources of the same redmine, it simply executes, for example, 'svn log', parses the result and compares it with what is stored in its database. If there are differences, it starts adding all the necessary data to the database. But the bottom line is that he simply executes commands in the shell and parses the result.