Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Types of Locks
There are two necessary types of locks:
Let us first take an instance for binary locking and describes how it solves the concurrency related troubles. Let us reconsider the transactions T1 and T2 for this purpose; though we will add to needed binary locks to them.
Schedule
T1
T2
Lock X
Read X
Subtract 100
Write X
Unlock X
Lock Y
Read Y
Display X+Y
Unlock Y
Add 100
Write Y
Figure: An incorrect locking implementation
Does the locking as completed above solve the problem of concurrent transactions? No the similar problems still remains. Try working with the old value. Therefore, locking should be completed with some logic in order to make sure that locking results in no concurrency related problem. One such answer is given below:
Lock X (issued by
T2)
Lock X: denied as T1 holds the lock.
The transaction T2 Waits and T1 continues.
The lock request of T2 on X can now
be granted it can resumes by locking X
Figure: A correct but restrictive locking implementation
Therefore, the locking as above when you get all the locks at the starting of the transaction and release them at the end ensures that transactions are implemented with no concurrency related problems. Though, such a scheme limits the concurrency. We will talk about a two-phase locking method in the next subsection that gives sufficient concurrency. Though, let us first discuss multiple mode locks.
What is the full form of DDL? DDL is stand for Data Definition Language.
What is a hash index? A hash index organizes the search keys, with their associated pointers, into a hash file structure.
Briefly explain each of the following database terms. Use no more than 2-3 lines for each term. 1. DBMS 2. Update Anomaly 3. Alias (referring to tables in SQL queries)
Define the terms i) DDL ii) DML DDL: Data base schema is specified by a set of definitions expressed by a special language known as a data def
compare the features of oracle RDBMS with MySQL and Microsoft SQL server
We face problem of stock Opening balance and closing balance in Minus
Define Atom of domain relational calculus An atom has the outline 1 , x 2 , ... , x n > -> r , in which r stands for a relation on n attributes and x 1 , x 2 , ... , x n ar
for the following business rules . Identify all entities, attributes, relationships, primary keys, cardinalities and constraints where appropriate 3. (9) An art museum owns a larg
An employee record has the following structure struct employee { int eno; char name[22]; float salary; char dept[10];}; (i) Calculate the record size R in bytes.
read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd