4.1.23. Dirty read (or Temporary update)

  • T1
  • read_item(X);
  • X=X-N;
  • write_item(X);


  • <T1 fails>
  • <T1 rollback>


  • read_item(X);
  • X=X+N;
  • write_item(X);
  • T2


  • read_item(X);
  • X=X+M;
  • write_item(X);
  • T2 reads temporary incorrect value of X