5. Transactions Flashcards
A transaction is a unit of program execution that ___ and possibly ___ various data items.
Accesses
Updates
ACID stand for ___ ___ ___ ___
Atomicity Consistency Isolation Durability
Atomicity
Either all operations of the transaction are properly
___ in the database or ___
Reflected
None are
Consistency
Execution of a transaction in ___ preserves the consistency of the database.
Isolation
Isolation
Although multiple transactions may execute concurrently, each transaction must be ___ of other concurrently executing transactions. Intermediate transaction results must be ___ from other concurrently executed transactions.
Unaware
Hidden
Durability
After a transaction completes successfully, the changes it has made to the database ___, even if there are ___.
Persist
System failures
Schedule
A sequence of instructions that specify the
___ in which instructions of ___
transactions are executed
Chronological order
Concurrent
Serializability (Basic Assumption)
Each transaction preserves database ___
Consistency
Conflicting Instructions
Instructions l_i and I_j of transactions T_i and T_j
respectively, conflict if and only if there exists some ___ Q accessed by both l_i and l_j , and at least one of these instructions ___ Q.
Item
Wrote
Conflict equivalent
Schedules S and Sā are conflict equivalent if a S can be transformed into Sā by a series of ___
Non-conflicting instructions
Conflict serializable
Schedule S is conflict serializable if it is ___ to a ___ schedule
Conflict equivalent
Serial
Recoverable schedule
If transaction Tj reads a data item previously written by a transaction Ti , then the commit of Tj must appear ___ the commit of Ti
After
Cascading rollback
A ___ transaction failure leads to a series
of ___
Single
Transaction rollbacks
Isolation Levels 1- \_\_\_ 2- \_\_\_ (Phantom Reads) 3- \_\_\_ (Phantom Reads / Non-repeatable reads) 4- \_\_\_ (Phantom Reads/ Non-repeatable reads /Dirty Reads)
Serializable
Repeatable read
Read committed
Read uncommitted
