The problem arise when:
- there is a lot of users in one project (~1000)
- there is a lot of user groups in this project (~200)
- there is a few svn repositories (~20)
The system event that will update the svn access file will take up to 30mn to be processed.
In addition to that, each and every user group modification will lead to a re-generation of the svn access files. Example: removing one user from project that is member of 10 user groups => 5 hours to process everything.
There are probably some low hanging fruits to make it faster.