unit 7: distributed concurrency control

Question 1

define transaction

Answer 1

A transaction can be defined as a unit or a part of program at the time of its execution,
that forms logical unit of database processing…

hamare pas bohot sari lines of cod e/ program hota he, usme se ham at a time kisi ek line ko hi to execute karenge to uss part ko ham transaction kahenge

Question 2

can transaction includes one or more access operation on database

Answer 2

Yes, transaction can include one or more access operations on a database like, insertion, deletion, modification or retrieval operation

Question 3

why understanding transaction’s is important

Answer 3

all things are related to transactions in this subject
thats why understanding transactions is very important

Question 4

what are some basic database access operations

Answer 4

1. read_item( x )
2. write_item( x )

Question 5

Is there any similarity between Transaction or Process ?

Answer 5

In DBMS, part or unit of program is known as Transaction

In OS, part or unit of program is known as Process

Question 6

Why ACID properties are used?

Answer 6

To maintain the integrity of program we use ACID properties.

For ensuring integrity of data, database system maintain the ACID properties.

Question 8

what is schedule?

Answer 8

whenever multiple transactions are operating, each and every transaction has to done certain set of actions, so at which instant of time, which action, under which transaction is going to get executed, that will be mapped along with time instant and that is known as schedule.

Question 9

example

Answer 9

there are two transaction T1 and T2 in schedule

this transaction has to do 4 tasks/actions

some read write operation, it is being guided by begin_tran and commit, in this brackets this transaction is carried out

for T2 there are also some transaction

Question 10

what is serial schedule

Answer 10

a schedule where the operations of each transaction are executed consecutively without any interleaved operations from other transaction

Question 11

non-serial schedule

Answer 11

a schedule the operations from a set of concurrent transactions are interleaved

Question 12

testing of serializabilty

Question 13

concurrency control definition / understanding

Answer 13

In real life situations (applications) multiple transactions will be executed in parallel or concurrently

Question 14

what will happen if there is no concurrency control

Answer 14

those transaction execution will leave behind database, in some inconsistent state

Question 15

Proper definition of concurrency control

Answer 15

the concurrency control is a process of managing simultaneous operations on the database without having them interfere with one another. It enhances overall CPU utilization.

Question 16

there are 3 potential problems of concurrency

Answer 16

• lost update problem
• uncommitted dependency (or dirty read) problem
• inconsistent analysis problem

Question 17

what are other words use for concurrency

Answer 17

parallelly / simultaneously / at same time

Question 19

what / explain granularity of locks
[first concept in lock based protocols]

Answer 19

the level and type of information that the lock protects is called locking granularity

OR

in other words, the size of data item that the data manager locks is called locking granularity

Question 20

Lost update problem Explain

Answer 20

update operation of one user is overwritten by another user

OR

If any transaction Tj updates any variable A at time t, without knowing the value of A at time t , then this may leads to lost update problem

Question 21

example of lost update problem

Question 22

example of lost update problem

Answer 22

user one initiated T1
user two initiated T2

T2 is older, because it got initiated at t1
T2 is younger, initiated at t2

so the updates done on balX are overwritten by T2

That is our lost update problem

Question 23

Explain uncommitted dependency / dirty read problem

Answer 23

when a transaction uses result of partially completed transaction

OR

Reading the data value of a variable before committing may lead to ‘Dirty Read Problem’

OR

ek transaction kisi variable par kam kar raha tha, hi transaction commit honachya pahile, dusrya transaction ne hya variable cha data read kela

Question 25

explain inconsistent analysis problem

Answer 25

when a transaction reads several values from the database but a second transaction updates some of them during the execution of the first

Question 26

Explain locking

Question 27

Methods of Locking

Question 28

Explain shared lock

Question 29

explain exclusive lock

Question 30

Explain two phase lock / 2 PL

Question 31

how 2PL can be used to prevent lost update problem

Question 32

how to prevent uncommitted dependency problem

Question 33

how to prevent inconsistent analysis problem using 2Pl

Question 34

Explain cascading rollback problem using 2Pl

Question 35

granularity of data items

Answer 35

whenever multiple transactions are taking place, concurrently then there is a problem there is interference of data.

One transaction update is getting cancelled nullified by other transaction

so our data require protection, and this protection can be obtained from concurrency protocol

Question 37

from this -

Answer 37

separate

Question 38

what does distributed concurrency control mechanism ensures

Answer 38

It ensures consistency of database in multi-user distributed environment

Question 39

what is mean by concurrent execution of transactions

Question 40

what is conflicting operations

Question 41

how to classify concurrency control mechanism