# dbms DIRTY READ

Question

Please explain the concept of DIRTY READ In a simplified manner w/ a small example! 

Comments

reading data written by an uncommitted transaction.

T1     T2

w(A)  

          r(A)

above is example of dirty read. If T1 commits after writing A, then it is not dirty read by T2.
Tell me if I missed something.

Answer 1

In one statement :

Reading uncommitted data.

Say T1 is writing any variable x

Concurrently running, a transaction T2 requires the value of x

T1                        T2

write(x)         

                          read(x)

                          commit

failure

Now, when T1 fails, it is rolled back and the modified value of x is lost. The database still has the previous value which was last committed by any other transaction. However, T2 completed and got committed using the wrong value of x it might use in calculations. This is said as Dirty read problem.

Comments

@ gauravkc

IN the above example taken by you is w₁(x) a producer?

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Who is a producer in database?