Transaction Isolation
Transaction Isolation means, when there are two transitions that are taking place simultaneously, then one transaction should not overlap the other. Each translation should not be aware of the other transactions currently taking place in the system. The database should take care of the control over the concurrent transactions. Transactions use ACID properties for Isolation.
We will be understanding “Transaction Isolation” with the help of examples.
Take the following transaction.
Transfer an amount of Rupees 50 from Account-A to Account-B.
T1 : read A ;
A = A – 50 ;
write A ;
read B ;
B = B + 50 ;
write B ;
Example-1 :
Consider the T1 transaction from Example-1 :
T1 : read A ;
A = A – 50 ;
write A ;
read B ;
B = B + 50 ;
write B ;
Let transaction T2 transfers 10 % of the amount from Account-A to Account-B.
T2 : read A ;
temp = A * 0.1 ;
A = A – temp ;
write A ;
read B ;
B = B + temp ;
write B ;
‘Schedule’ is a set of transactions to be executed sequentially or concurrently.
Let the current values be
Account-A = 1000
Account-B = 2000
Example-2 : Create a Schedule-1 such that transaction T1 is followed by transaction T2.
| T1 | T2 |
| read A ; A = A – 50 ; write A ; read B ; B = B + 50 ; write B ; commit | |
| A = A – temp ; write A ; read B ; B = B + temp ; write B ; commit |
Here, the values of A and B initially are : 1000 and 2000.
| A | B | |
| Initial Values | 1000 | 2000 |
| After T1 | 950 | 2050 |
| After T2 | 855 | 2145 |
Here, the value of temp = 95.
Also, before and after Schedule-1, A + B values are the same
Let’s understand the further concepts in Transaction Isolation using the same example. Refer to the next article for better understanding of transaction Isolation.
Reference Link.