More on Steal and Force
STEAL (why enforcing Atomicity is hard)
- To steal frame F: Current page in F (say P) is written to disk; some Xact holds lock on P.
- What if the Xact with the lock on P aborts?
- Must remember the old value of P at steal time (to support UNDOing the write to page P).
NO FORCE (why enforcing Durability is hard)
- What if system crashes before a modified page is written to disk?
- Write as little as possible, in a convenient place, at commit time,to support REDOing modifications.