Transactions Flashcards
What is a transaction?
A unit of program execution that accesses and possibly edits various data items.
Expand ACID.
Atomicity
Consistency
Isolation
Durability
Name the 5 transaction states.
Active Partially Committed Failed Aborted Committed
Define schedules.
Sequences that indicate the chronological order in which instructions of concurrent transactions are executed.
When is a schedule serializable?
When it is equivalent to a serial schedule.
What is conflict equivalence?
When S can be turned into S’ by a series of swaps of non conflicting instructions.
When is a schedule S conflict serializable?
When it is conflict equivalent to a serial schedule.
When are two transactions view equivalent?
When following three conditions are met:
- S and S’ read initial values.
- If S reads a value of Q produced by Tj, S’ should too.
- The transaction that performs final write(Q) in S must do same in S’.
What is a recoverable schedule?
When a transaction Tj reads data items previously written by Ti, the commit of Ti appears before commit of Tj.
What is a cascading schedule?
A schedule in which transaction are dependent on other transactions in schedule.
What is cascading rollback?
The phenomenon in which single transaction failure lens to a series of transaction rollbacks.
When is a schedule conflict serializable?
When precedence graph has no cycles.
