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Strict 2PL:Though, this basic 2PL suffers from the trouble that it can result into loss of isolation / atomic property of transaction as theoretically speaking once a lock is released on a data item it can be changed by another transaction before the first transaction aborts or commits.
To leave such a situation we use strict two phase locking. The strict 2PL is graphically depicted in Figure. Though, the basic drawbacks of strict 2PL are that it restricts concurrency as it locks the item afar the time it is required by a transaction.
Figure: Strict Two Phase Locking
Does the two phase locking solve all the problems of concurrent transactions? No, the strict 2PL answers the problem of concurrency and atomicity, though it introduces another problem.
Define entity integrity and referential integrity. How does SQL allow specification of these? Ans: Entity Integrity Rule- If the attribute A of relation R is a prime attribut
Example :; transfers transfer_amount from x's account to y's account ; Supposes x&y both accounts exist TRANSACTION (x, y, transfer_amount) Start transaction IF X AND Y
Which is another name for weak entity? Child is another name of weak entity.
How does Tuple-oriented relational calculus vary from domain-oriented relational calculus? The tuple-oriented calculus uses a tuple variables i.e., variable whose only allowed
i need help for assignment ..
(a) Why did SAP introduce the extended star schema?
Vertical Fragmentation- Vertical fragmentation groups together only those attributes in a relation that are used jointly by various important transactions. A vertical fragment is d
Having Clause with sub queries: First we have to recollect the GROUP BYclause. The following query searches the minimum salary in every department. SELECT DEPTNO, MIN (SAL)
What is Identity? Identity (or AutoNumber) is a column that automatically produces numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID
Describe Hashing in DBMS? Hashing: Hashing is a technique to store data within an array so which storing, searching, inserting and deleting data is fast (in theory it's O(1))
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