More Conflicts

• RW Conflicts (Unrepeatable Read)

  • T2 overwrites what T1 read.
  • If T1 reads it again, it will see something new!
    • Example when this would happen?
    • The increment/decrement example.
  • Again, not equivalent to a serial execution.

• WW Conflicts (Overwriting Uncommited Data)

  • T2 overwrites what T1 wrote.
    • Example: 2 Xacts to update items to be kept equal.
  • Usually occurs in conjunction w/other anomalies.
    • Unless you have “blind writes”.

Previous slide

Next slide

Back to first slide

View graphic version