The Log
A sequential file of records describing updates:
- address of updated page
- id of transaction that did the update
- before-image and after-image of the page
Whenever you update the cache, also update the log
Log records for Commit(Ti) and Abort(Ti)
Some older systems separated before-images and after-images into separate log files.
If opi conflicts with and executes before opk, then opi’s log record must precede opk’s log record
- recovery will replay operations in log record order