Unit 06 Flashcards
abort
Deliberately stop something that has started.
Aborted (transaction state)
The state a transaction is in after it has been rolled back to undo any partially completed actions of the transaction.
ACID properties
The desirable properties of a transaction: Atomicity,
Consistency,
Isolation and
Durability.
acquire phase
The phase in two-phase locking in which the locks are gradually acquired, and in which no locks can be released.
See also release phase
Active (transaction state)
The state a transaction is in as soon as it has started, and in which it remains while executing.
after image
In logging, the name given to the value of a variable after an update is made.
asymmetric replication
A style of ownership of data in schemes for replication of data where data is owned by the master site, and only the master site is allowed to make updates to the data.
See also master–slave ownership.
asynchronous replication
A strategy for replication of data, in which a replicated part is updated some time after the source database is updated.
before image
In logging, the name given to the value of a variable before an update is made.
cache manager (in a transaction processing system)
The part of the transaction processing system that organises the objects in main memory and interfaces with the persistent storage.
cascade of aborts
The situation where a transaction has had to be aborted, and this in turn leads to many other transactions having to abort.
commit protocol
A protocol to commit transactions.
See two-phase commit (2PC) protocol.
Committed (transaction state)
The state a transaction is in after the transaction has completed successfully and all the updates to the data have been made permanent (persistent).
conflicting operations
Two operations A and B are said to be conflicting if, starting from some initial state, the result of executing A then B is not the same as the result of executing B then A. Also known as non-commutative operations.
coordinator
In the two-phase commit protocol for distributed transactions, the process that oversees the activities of other participating processes, each of which is dealing with only part of a transaction.
crash resilience
The extent to which an application is supported in recovering from system crashes.
data replication
Holding multiple copies of data items in different locations.
database
In computing, a structured collection of records or data that is stored in a computer so that a program can consult it to answer queries.
database driver
The implementation details of a particular database are handled by the database driver for that database.
database management system (DBMS)
The computer program used to manage and query a database.
database metadata
Literally, data about data. For example, data about the vendor of the database system and data about the way the database records are stored.
directed acyclic graph (DAG)
In graph theory, a graph with nodes and edges, where each edge has a definite direction (going from one node to another). The graph has no cycles, meaning that there is no path from a node that leads back to itself.
dirty read
A dirty read occurs if a transaction reads values that are written by another transaction that has not committed yet.
exclusive lock
A lock that needs to be acquired by a writer process. Only one process can hold a write lock at the same time.
Also referred to as a write lock.
externally visible effect
Any communication that an operation may have with another process, user or storage device.
Failed (transaction state)
The state a transaction is in when the discovery is made that normal execution cannot proceed.
failure atomicity
A form of atomicity, also known as all-or-nothing atomicity, which is one of the properties of a transaction. It refers to the fact that if there is some kind of failure which causes a part of the transaction not to be completed, then the entire transaction should be rolled back.
failure transparency
Another term for crash resilience, referring to a system’s ability to create the illusion that a failure never happened.
fragmentation
Slicing a database into different fragments, such that each part is stored in different physical areas of storage.
global transaction
A transaction that accesses and updates data in several databases
(contrast with local transaction).
granularity of a lock
A design consideration for algorithms based on locks, regarding the size of the object that needs to be locked.
intermediate state
The state that a system is in while it is in the middle of executing an operation. In transaction processing it is desirable that other concurrent transactions avoid seeing the intermediate state of a given transaction.
Java Transaction API (JTA)
A standard Java interface for demarcating transactions.