- Transaction processing:
- A transaction is
atomic:
- All updates made by
a transaction will be made
permanent
or
- All updates made by a transaction will be voided
- All updates made by
a transaction will be made
permanent
or
- Methods/techniques to
achieve
atomicity despite of
failures:
- Undo log
- Redo log
- A transaction is
atomic:
- Problem:
- A failure is assumed
to stop the
entire system
- This assumption is no longer true in a distributed database system !!!
- A failure is assumed
to stop the
entire system
- Consider a
distributed database:
- A transaction T is
initiated at
site 1:
-
Transaction T will
spawn
components running at
other site to
perform updates of the
stored fragments:
- Distributed transaction processing:
- How to
ensure the
atomicity (=
all or nothing) of the
execution
of a transaction
on a distributed database:
- All component processes of
transaction T must
commit (and make
updates
permanent)
or
All component processes of transaction T must abort
- All component processes of
transaction T must
commit (and make
updates
permanent)
or
Problem scenario:
- A failure occurs
at one
of the processing sites:
Result:
- A partial set of updates will be incorporated into the distributed database !!!
- How to
ensure the
atomicity (=
all or nothing) of the
execution
of a transaction
on a distributed database: