Test Series closed

Question

Question:

Consider the following transactions:

The number schedules of T₁ and T₂ recoverable are ________.

Comments

transactions are not visible

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Updated!

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is it 33?

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I write T1 with blank spaces in b/w every operation.
 __W(A)__W(B)__R(C)__c1__

Dirty read means reading uncommitted data.
Dirty read will be there when R(B) and c2 of T2 will be after W(B) of T1 AND before c1 of T1.
Note:

1.If R(B) of T2 is after W(B) of T1 and c2 comes after c1 then that is recoverable.
2.W(B) of T2 should not come after W(B) of T1. W(B) of T1 should be succeeded by R(B) only for dirty read case.

Case 1: __W₁(A)__W₁(B)  *R₂(B)*  R₁(C)   *c2*  c1__

W₂(B) can be present in any one of the two blanks before W₁(B). So 2 ways.

Case 2: __W₁(A)__W₁(B) *R₂(B)*  *c2*  R₁(C)__c1__

W₂(B) can be present in any one of the two blanks before W₁(B). So 2 ways.

Case 3:__W₁(A)__W₁(B)__R₁(C)  *R₂(B)*  *c2* c1__

W₂(B) can be present in any one of the two blanks before W₁(B). Here don't keep W₂(B) after W₁(B) otherwise it won't be a "dirty read".So 2 ways.

If c2 comes after c1 then that is recoverable.

Total no. of schedules possible is 7!/(4! * 3!) =35.
There are 3 cases only where dirty read can happen. Only these 6 cases will be responsible for non-recoverable schedule. So 35-6=29.

Shaik Masthan Please check if this is correct or not.

 

 

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@MiNiPanda, yes... you are right... i miss one variable.. it leads to 2 sequences... it is 31, check iamkoushal21 solution

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i was getting these 6 Ir-recoverable, so i think 29 Is answer. Sorry forgot to upload last night. verify this please. 

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@iamkoushal21, yes it should be 31

W₁(A) ---- has 2 choices

R₁(C) ---- has 2 choices

total 4 ir-recoverable schedules possible....

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Shaik Masthan I have edited my previous comment. Can you please check it ? I am getting 29 now :/

Also i commented here yesterday but i can't see it anymore  :O

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@MiNiPanda,

Case 3:__W₁(A)__W₁(B)__R₁(C)  *R₂(B)*  *c2* c1__

it is not dirty read.... 

dirty read means, there is no operation is allowed in between W1(B), R2(B).

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But the data items are different right?

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ya...  forgetted the basic point... sorry for that

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why W(B) of T2 should not come after W(B) of T1 ?

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@jatin kumar 3

IT IS CLOSED.... you go to the link which provided at closing tag and check the answer, still any doubt then comment.