Given the following code SQL: what will return the sentence select of the row 8 (transaction T2) 10 20 an exception will happen in T1 an exception will happen in T2.
Given two transactions T1 and T2 and the below execution plan, we can affirm At a level of isolation READ UNCOMMITED a dirty reads would happen At a level of isolation READ UNCOMMITED a phanton reads would happen At a level of isolation READ COMMITED a dirty reads would happen At a level of isolation READ COMMITED a phanton reads would happen.
In Oracle, a serializable transaction: It can generate an exception if it tries to modify a data that has been modified in another transaction T2, after beginning T1 It can read not updated data It is the minimal level of necessary isolation to guarantee that there will not be dirty reads It is the minimal level of necessary isolation to guarantee that there will not be phantom reads.
Given two transactions T1 and T2 and a schedule P, it is possible to guarantee that: If P is serializable, it is guaranteed that there are not conflict operations If P is serial, it is guaranteed that that there are not conflict operations If P2 is an alternative schedule to P, P2 is serial, it is known that both obtain the same database state at the end of the execution plan If P is serial then it is strict.
Taking the following case as an example, write a schedule to be: NO SE CUAL ES Serial and strict Serializable and not serial, recoverable and that avoids delete in cascade Serializable and not serial, strict Not serializable and it does not avoid delete in cascade Serializable and not recoverable.
A planner that implements the protocol of strict 2PL It guarantees that any schedule will be serializable It guarantees that any schedule will be recoverable It guarantees that there will not be deadlocks It guarantees that no transaction will stay in indefinite waiting.
A planner that guarantees concurrence, the serializability, prevents deletes in cascade, is not free from of deadlocks and does not
know the data that every transaction is going to modify to the beginning of this one, might implement a strategy: Serial Conservative 2PL Strict 2PL Rigorous 2PL.
With regard to Oracle SERIALIZABLE isolation level, it is posible to affirm: It prevents lost updates It prevents cascade deletes It prevents deadlocks It is a 2PL strategy.
With regard to Oracle READ COMMITED isolation level, it is possible to affirm: It prevents lost updates It prevents erasures in cascade It prevents deadlocks It prevents dirty readings.
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