Recovery

Question 1

what is log based recovery?

Answer 1

• a log is kept on stable storage
• when a transaction starts, it registers itself on the log
• before a write, the transaction writes to the log with the value before and after the change
• write commit to log when complete

Question 2

what is deferred database modification?

Answer 2

a log approach

• writes to the log deferred to after a partial commit
• then, during recovery, a transaction needs to be redone only if start and commit are both in the log

Question 3

what is immediate database modification?

Answer 3

a log approach
- allows database updates of an uncommitted transaction to be made as the writes are issued
- need to keep track of the previous values
- if transaction has both start and commit, redo
- if start but no commit, undo
-

Question 4

what is a checkpoint?

Answer 4

a checkpoint in a log marks that everything prior has been flushed to disk
avoids us going through stuff unnecessarily

Question 5

what is shadow paging?

Answer 5

an alternative log-based stuff

two page tables that represent data

• current pages
• shadow pages

the shadow page is always consistent

the current includes the transactions in process

when a page is about to be written, copy it
the current points to the copy, shadow to the original#
make changes to the copy, update shadow pointer to the copy

DOESNT WORK WITH CONCURRENT TRANSACTION