in Databases
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2 votes
2 votes
T1 T2 T3 T4
  R(X)    
    W(X)  
    C3;  
W(X)      
C1;      
  W(Y)    
  R(Z)    
  C2;    
      R(X)
      R(Y)
      C4;

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Doubt: Transaction T3 is commited before T1 and w-w problem.This results is there any edge between T3 and T1 in precedence graph or not??

in Databases
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1 Answer

5 votes
5 votes
Best answer

Problem comes when there is an edge between

a) Two transactions which ar different

b) The pair is either read write , or write read or write

c) On the same data item

d) The earlier of the two should be uncommitted as the problem does not come on committed transactions.

Keeping in mind the above points , we have following conflict pairs :

a) T2 - T1

c) T2 - T3

edited by

4 Comments

Corrected bro..:) My mistake..
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k got now :) thanku @Habib and @santhos.
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edited by

@habib i am not getting your 4th point ...

take this example  this schedule is not serizable to any serial schedule becuase  T2 is reading a data item  A which is writen  by T1 (T1-T2). so scheduling should be T1 to T2 but prbolem is this  T2 is reading the data item B  which is initial value of B so by this schedulig  must be( T2-T1) so schedule is not serizable to any serial schedule. and this problem will  exist  if T2 is commited or not commited ..

you can give me any Referece for 4th point ?

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