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INTRO. TO DATABASE MGMT. SYST.
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In a WAL system, which of the following must happen before a dirty data page is written to disk?
The no-force policy allows faster commit of transactions compared to force policy.
In the wait‐die deadlock avoidance scheme, older transactions never wait for younger ones.
Consider the following schedule.
T1 | T2-----------+------------ | | lock-S(A) : request lock and lock was granted | read(A) lock-X(A) | : T1 requests a lock held by T2 Assume that TS(T1) < TS(T2), then under the wound‐wait deadlock scheme
Consider the following schedule
| T1 | T2+------------------+------------------| BEGIN | | READ(A) | | A = A + 50 | | WRITE(A) | | | BEGIN| | READ(A)| | A = A + 200| | WRITE(A)| | READ(B)| | B = 3 * B| | WRITE(B)| | COMMIT| READ(B) | | B = 12 * B | | WRITE(B) | | COMMIT |
In validation‐based concurrency control, which phase checks whether a transaction can safely commit without violating serializability?
Consider the following transaction schedule. Indicate if it is conflict-serializable or not:
| T1 | T2 | T3+--------+---------+--------| read(A). | | | | read(B) | | | | read(A) | | read(A) | | | | read(C) | read(B) | | | | | read(B) | read(C) | | | | read(C) | | commit | | | | commit | | | | commit
Optimistic (validation‐based) protocols tend to perform better than locking protocols in environments with low contention.
Recall that a shared lock may be held by several transactions, while an exclusive lock can be held by only one transaction. Consider two systems• System A uses shared and exclusive locks.• System B uses only exclusive locks.
Then,
In strict two‐phase locking (S2PL), when are all locks released?