GATE CSE 2009
Q41.
Consider two transactions T1 and T2, and four schedules S1, S2, S3, S4 of T1 and T2 as given below: T_{1}:R_{1}[x]W_{1}[x]W_{1}[y] T_{2}:R_{2}[x]R_{2}[x]W_{1}[y] S_{1}:R_{1}[x]R_{2}[x]R_{2}[y]W_{1}[x]W_{1}[y]W_{2}[y] S_{2}:R_{1}[x]R_{2}[x]R_{2}[y]W_{1}[x]W_{2}[y]W_{1}[y] S_{3}:R_{1}[x]W_{1}[x]R_{2}[x]W_{1}[y]R_{2}[y]W_{2}[y] S_{4}:R_{2}[x]R_{2}[y]R_{1}[x]W_{1}[x]W_{1}[y]W_{2}[y] Which of the above schedules are conflict-serializable?Q42.
While opening a TCP connection, the initial sequence number is to be derived using a time-of-day (ToD) clock that keeps running even when the host is down. The low order 32 bits of the counter of the ToD clock is to be used for the initial sequence numbers. The clock counter increments once per millisecond. The maximum packet lifetime is given to be 64s. Which one of the choices given below is closest to the minimum permissible rate at which sequence numbers used for packets of a connection can increase?Q43.
Let R and S be relational schemes such that R={a,b,c} and S={c}. Now consider the following queries on the database: I.\pi _{R-S}(r)-\pi_{R-S}(\pi_{R-S}(r) \times S -\pi_{R-S,S}(r)) II.\{t|t\in \pi _{R-S}(r)\wedge \forall u \in s (\exists v \in r(u=v[s]\wedge t=v[R-S]))\} III.\{t|t\in \pi _{R-S}(r)\wedge \forall v\in r(\exists u\in s(u=v[s]\wedge t=v[R-S]))\} IV. Select R.a, R.b From R,S Where R.c=S.c Which of the above queries are equivalent?