Labs 6 - Multiple granularity, timestamp, and validation-based protocols.
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Exercises
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(1) The operations of transactions T1, T2, T3 arrive at the scheduler in the
    order shown on the following schedule. Simulate a timestamp-based scheduler
    and insert aborts when required.

    T1:       T2:       T3:
    read(X)
              read(Y)
                        read(X)
              read(X)
                        write(X)
              write(Y)
              write(X)
    read(Y)

(2) Consider a timestamp-based scheduler and transactions T1, T2, TS(T1)=3, 
    TS(T2)=4. Furthermore, assume that the data items X and Y have last been 
    read and written by a transaction with timestamp 1. Describe each step taken
    by the timestamp-based scheduler.

    T1:       T2:
    read(X)
    read(Y)
              read(Y)
              read(X)
    write(Y)
              write(X)

(3) Is the following schedule possible under a timestamp-based ordering protocol?
    (TS(T1)=1, TS(T2)=2, TS(T3)=3)

    T1:       T2:       T3:
              read(Z)
              read(Y)
              write(Y)
                        read(Y)
                        read(Z)
    read(X)
    write(X)
                        write(Y)
                        write(Z)
              read(X)
    read(Y)
    write(Y)
              write(X)

(4) A database has two (R)elations, each relation has two (T)uples, and each 
    tuple has two (A)ttributes. Draw the database elements in a hierarchy. 
    Assuming that no locks are released, indicate the locks acquired by each of 
    the following transactions executed in the given order.

    T1: Update A1 of T1 of R1.
    T2: Update A2 for all tuples in R2.
    T3: Read all tuples of R1.

(5) Consider the database with the following two relations:

    (M)ovies[mid, title, year, avg_rating]
    (A)ctors[mid, name]

    Organize the database elements in a hierarchy. For each of the following 
    queries, indicate the sequence of lock and unlock operations issued by a 
    transaction executing a single query.

    Q1: Change the tiles of all movies to capital letters.
    Q2: What is the rating of the movie "Minions"?
    Q3: List all the actors.
    Q4: Compute the average rating of all movies published in 2014.
    Q5: Reset the ratings of all movies filmed in 2000.

(6) Consider the following two schedules. Indicate what happens when each 
    schedule is processed by a validation-based scheduler.

    Schedule 1
    --------------------------------
    T1:         T2:         T3:
    read(A,B)
                read(B,C)
                            read(C)
    validate
                validate
                            validate
    write(A)
                write(B)
                            write(C)

    Schedule 2
    --------------------------------
    T1:         T2:         T3:
    read(A,B)
                read(B,C)
                            read(B)
    validate
                validate
    write(C)
                            validate
                write(B)
                            write(C)