User written transaction code is responsible for the “C” in ACID

transactions, i.e., taking the database from one consistent state to

the next. However, user transactions can be flawed and lead to

inconsistent (or invalid) states. Database systems usually correct

invalid data using “point in time” recovery, a costly process that

installs a backup and rolls it forward. The result is long outages

and the “de-commit” of many valid transactions, which must then

be re-submitted, frequently manually. We have implemented in

our transaction-time database system a technique in which only

data tainted by a flawed transaction and transactions dependent

upon its updates are “removed”. This process identifies and

quarantines tainted data despite the complication of determining

transactions dependent on data written by the flawed transaction.

A further property of our implementation is that no backup needs

to be installed for this because the prior transaction-time states

provide an online backup.

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