I wrote that style of session mapping for a project long ago. It was fairly easy, but a massive pain in the ass to debug. Ended up needing to record the mappings in the backend for a period of time.
I too coded that in my server. It's not hard to do, and debugging can be harder at times (but not excessively so.) As you say it's just a case of logging when debugging.
When anchors are needed I use a different column for that- not the primary index. (Usually some other unique, already-present, value like the sku or whatever.
The security implications though are substantial. I don't leak primary key info even if the PK is serialized. (These days I'm all-in on UIDS but I have older legacy systems to deal with too.)
