Assignment handed out on Wednesday, March 14, 2001
Due in Recitation on 3/15/2001:
Read Chapter 12 from the text. Focus on sections 12.2-12.4. Also
read The Design and Implementation of a Log-Structured File
System. Your writing/discussion assignment:
Suppose you were implementing transactions, for a banking system. Due
to the nature of the application, you assume that the read:write ratio
on accounts will be close to 1:1 (e.g., deposits and withdrawals, the
most common transactions, require reading the balance, then writing it
back out. Locks require a test and a set.).
You've read that a Log-Structured File System is supposed to increase
write efficiency, so you decide to consider it as your system's file system.
One huge consideration is implementing your commit procedure. For
this procedure to work, you need to make sure that LFS won't lose your
writes. It looks like LFS has two recovery mechanisms - Checkpoints
and Roll-Forwards. Checkpoints appear to be more robust than
Roll-Forwards. Describe why this is, and the key tradeoff(s). What
system parameter could you alter to increase the granularity of
If relying solely on Checkpoints was not practical, how would you approach
using Roll-Forwards to implement commit, so that your committed transactions will not
disappear if the server unexpectedly shuts down?
Hint: Consider at what point during a file write the data
becomes recoverable under Roll-Forward.