15 terms

Transactions

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Terms in this set (...)

ACID
Atomicity
Consistency
Isolation
Durability
Atomicity
Database operations must be entirely completed or aborted
Consistency
Must take a database from one consistent state to another
Isolation
Must not interfere with other concurrent transactions
Durability
Once completed, changes are durable (in cases of system failure)
Writing Schedules
Read
Write
Commit
Abort
Serial Schedule
A whole transaction is completed before anotherone
Interleaved Schedule
Transactions can be done at the same time (depending on locks)
Lock Types
Shared (Read)
Exclusive (Write)
Deadlock
2 transactions have a lock on the resource required by the other
Deadlock Prevention
A transaction must acquire all locks it requires before updating any record
Victim Selection
Which transaction is aborted (less updates, newer)
Transaction log
A log which tracks all transactions that update the database
Checkpointing
Accepting new transactions halted, and transactions are suspended. Results of committed transactions are force written to disc. A checkpoint record is written in the log
Write Through Policy
Database is immediately updated by transaction operations during transaction's execution, before the transaction reaches it's commit point. IF a transaction aborts before it reaches its commit point a Rollback or Undo operation is required to restore the database to a consistent state