Great video. You may not have millions of subscribers like some but the quality of this information is as good as anything else out there on RU-vid. I tip my hat to you good sir ;)
Why? It actually ever simple, you just have an append-only file which you are writing to it the old values of affected rows by every DML operation before applying those changes to actual data pages (the place you read data from). And if you have a crash, then read it in reverse with a rule: if the last appended record for a particular Transaction has COMMIT or ABORT value ignore it else apply those changes to actual data pages.
