read(y) - IBDS-OS Startseite

Consistency Predicate
BeginTransaction BeginTransaction
old_balance := if bank.read(“espen”) -
bank.read(“gerd”); bank.read(“gerd”) != $1M
new_balance := then CallTheSEC();
old_balance + $1M; EndTransaction(&commit)
bank.write(“espen”,
new_balance);
EndTransaction(&commit)
The above consistency predicate is quite simple:
“Espen always has 1 M$ more than Gerd”.
As long as one transaction’s operations happens entirely
before(after) the other, consistency is still valid.
SEC = Security and Exchange Commission
Transactions
However, interleaving of these operations might violate consistency!
1 Espens’s favorite bank
© 2009 Universität Karlsruhe, System Architecture Group 44