Recitation #3

*** Still not finished (but you can at least start...) ***

Paper Problems

1. r_1(x), r_2(x), w_1(x),w_2(x)

Write the DSG for the above schedule.
Is this schedule conflict serializable?
Is this schedule view serializable?

2. w_2(z),r_1(x),r_1(y),r_2(y),w_1(x),r_2(x),w_2(y),w_1(z),w_2(z)

Is this schedule conflict serializable?
Is this schedule view serializable?

3. Assume that the following schedule with locks is executed over a SVCC mechanism.

rlk_1(x), r_1(x), rlk_2(x), wlk_1(x),w_1(x),ulk_1(x),cmt_1, wlk_2(x),w_2(x),ulk_2(x), cmt_2

Describe what happens.
Does this schedule respect 2PL, SS2PL (AKA ‘Rigorous’), Conservative 2PL?  

4. Which SQL isolation levels are met with schedules that observe:
  a. locking protocols
  b. 2PL
  c. SS2PL (AKA 'Rigorous')
  d. Conservative and Rigorous

System Exercises 

Consider we have 2 runways and three time slots that planes may land. We represent this scenario in the following table: 

Two transactions (T_1 and T_2) want access to this table concurrently. In the problems that follow, always run T_1 before T_2, but start T_2 before T_1 commits, but after T_1 has executed its UPDATE operation. Use ps_sleep to automate this process. Always run the transactions over the initial state of the database above. For each of the transactions below, run under all 9 possible permutations of PostgreSQL isolation levels and group resulting behaviors into equivalence classes. (Isolation levels are READ COMMITTED, REPEATABLE READ, SERIALIZABLE). 

5. T_1: Book flight SK123 for runway 1 at time 1
    T_2: Book flight DY321 for runway 1 at time 1

6. T_1: Book flight SK123 for runway 1 at time 1
    T_2: Book flight DY321 for runway 1 at time 2

7. T_1: Book flight SK123 for runway 1 at time 1
    T_2: Set condition = 'rain' for runway 1 at time 1

8. T_1: Select the available runways for time 1, wait 20 seconds, and book the lowest number runway for SK123.
    T_2: Select the available runways for time 1, wait 20 seconds, and book the lowest number runway for DY321.

9. Define a PostgreSQL rule that guards against updates that allow for two flights being booked on the same runway in consecutive time steps.

10. Rerun problem 6 under with the rule of 9 defined.