CONCURRENCY CONTROL:

Verify that the following schedule is Degree 1 consistent but not degree 2
consistent: R1(X) R2(X) W2(X) R2(Y) W2(Y) R1(Y) W1(Y) Commit1 Commit2
Which transaction appears first in the (degree 1) equivalent serial schedule?

Create a schedule that is degree 2 consistent but not degree 3 consistent.

Can two different transactions hold an SIX lock on a file simultaneously?
Can two different transactions hold an IX lock on a file simultaneously?
Is an IS lock compatible with an X lock?
In each case, explain why in 1-2 sentences.

For a particular object A, the lock requests arrive as follows (in order):
t1(S), t2(S), t3(X), t4(S), t1(X), t5(S)
Show the various states of the lock queue as you "execute" a lock manager.
Draw a "time line" to show when specific transaction obtain and release locks
on object A.  Where multiple choices are possible, make one choice but
specify in words what the alternative(s) were.

Consider transaction t1 that reads X, writes Y, then tries to commit.
Transaction t2 reads Z, writes X and then tries to commit.
t2 finishes first, successfully validates, and commits through the optimistic
concurrent control manager.  When t1 arrives at the validation point, how
does the CC manager discover the potential conflict on X with t2?  Can t1 be
allowed to commit?