DBMS - Transactions and concurrency control

Question

I had a doubt.

In the case of lost update problem (special case of write – write problem, where a transaction commits to a blind write and the other transaction rollsback without commiting) , is the schedule recoverable or not??

Answer 1

In the case of lost update problem (special case of write – write problem, where a transaction commits to a blind write and the other transaction rollsback without commiting) , is the schedule recoverable ....

 

 

• Schedules in which transactions commit only after all transactions whose changes they read commit are called recoverable schedules...

• Concurrency control is the process of managing simultaneous execution of transactions (such as queries, updates, inserts, deletes and so on) in a multiprocessing database system without having them interfere with one another.

• This property of DBMS allows many transactions to access the same database at the same time without interfering with each other...

 

The primary goal of concurrency is to ensure the atomicity of the execution of transactions in a multi-user database environment...

Concurrency controls mechanisms attempt to interleave (parallel) READ and WRITE operations of multiple transactions so that the interleaved execution yields results that are identical to the results of a serial schedule execution….

The five concurrency problems that can occur in database are:

(i). Temporary Update Problem

(ii). Incorrect Summary Problem

(iii). Lost Update Problem

(iv). Unrepeatable Read Problem

(v). Phantom Read Problem

 

1. https://gateoverflow.in/240287/Transaction-cascadeless 

 

2. https://gateoverflow.in/102090/Dbms-schedules-lost-update-vs-ww-conflict 

 

3. https://gateoverflow.in/191804/Database-question-transactions 

 

4. https://gateoverflow.in/17082/Difference-between-strict-schedule-cascadeless-schedule?show=17085#a17085

 

 

Answer 2

Yes it is recoverable.
No dirty read is sufficient condition for schedule to be recoverable i.e if no dirty read exits then it is recoverable schedule but if dirty read exists it may or may not be recoverable.