ISDS 3110 Chapter 10
Glossary terms from Chapter 10
Terms in this set (44)
Atomic transaction property (Atomicity)
A property that requires all parts of a transaction to be treated as a single, logical unit of work in which all operations must be completed (committed) to produce a consistent database.
A lock that has only two states:
locked (1) and unlocked (0). If a data item is locked by a transaction, no other transaction can use that data item.
In transaction management, an operation in which the database management system writes all of its updated buffers to disk.
A DBMS feature that coordinates the simultaneous execution of transactions in a multiprocessing database system while preserving data integrity.
A database condition in which all data integrity constraints are satisfied. To ensure _ of a database, every transaction must begin with the database in a known consistent state. If not, the transaction will yield an inconsistent database that violates its integrity and business rules.
Consistent database state
A database state in which all data integrity constraints are satisfied.
The process of restoring a database to a previous consistent state.
The equivalent of a single SQL statement in an application program or a transaction.
A type of lock that restricts database access to the owner of the lock and allows only one user at a time to access the database. This lock works for batch processes but is unsuitable for online multiuser DBMSs.
Deadlock (Deadly Embrace)
A condition in which two or more transactions wait indefinitely for the other to release the lock on a previously locked data item.
Deferred update (Deferred-write technique)
In transaction management, a condition in which transaction operations do not immediately update a physical database.
In permanent storage, the equivalent of a disk block, which can be described as a directly addressable section of a disk. A _ has a fixed size, such as 4K, 8K, or 16K.
The transaction property that indicates the permanence of a database's consistent state. Transactions that have been completed will not be lost in a system failure if the database has proper _.
A lock that is reserved by a transaction. An _ is issued when a transaction requests permission to update a data item and no locks are held on that data item by any other transaction. An _ does not allow other transactions to access the database.
A lock that allows concurrent transactions to access the same row as long as they require the use of different fields (attributes) within that row. This type of lock yields the most flexible multiuser data access but requires a high level of computer overhead.
A database update that is performed immediately during a transaction's execution, even before the transaction reaches its commit point.
A concurrency control problem that arises when a transaction-calculating summary (aggregate)functions over a set of data while other transactions are updating the data, yielding erroneous results.
A property of a database transaction in which a data item used by one transaction is not available to other transactions until the first one ends.
A device that guarantees unique use of a data item in a particular transaction operation. A transaction requires a _ prior to data access; the _ is released after the operation's execution to enable other transactions to _ the data item for their own use.
The level of lock use. Locking can take place at the following levels: database, table, page, row, and field (attribute).
A DBMS component that is responsible for assigning and releasing locks.
A concurrency control problem in which data updates are lost during the concurrent execution of transactions.
A quality that ensures that timestamp values always increase. (The timestamping approach to scheduling concurrent transactions assigns a global, unique timestamp to each transaction. The timestamp value produces an explicit order in which transactions are submitted to the DBMS.)
Mutual exclusive rule
A condition in which only one transaction at a time can own an exclusive lock on the same object.
In transaction management, a concurrency control technique based on the assumption that most database operations do not conflict.
In this type of lock, the database management system locks an entire diskpage, or section of a disk. A diskpage can contain data for one or more rows and from one or more tables.
The use of locks based on the assumption that conflict between transactions is likely.
Redundant transaction logs
Multiple copies of the transaction log kept by database management systems to ensure that the physical failure of a disk will not impair the DBMS's ability to recover data.
A less restrictive database lock in which the DBMS allows concurrent transactions to access different rows of the same table, even when the rows are on the same page.
The DBMS component that establishes the order in which concurrent transaction operations are executed. The _ interleaves the execution of database operations in a specific sequence to ensure serializability.
A property in which the selected order of transaction operations creates the same final database state that would have been produced if the transactions had been executed in a serial fashion.
In transaction management, a schedule of operations in which the interleaved execution of the transactions yields the same result as if they were executed in serial order.
A lock that is issued when a transaction requests permission to read data from a database and no exclusive locks are held on the data by another transaction. A _ allows other read-only transactions to access the database.
A locking scheme that allows only one transaction at a time to access a table. A _ locks an entire table, preventing access to any row by transaction T2 while transaction T1 is using the table.
In transaction management, a technique used in scheduling concurrent transactions that assigns a global unique timestamp to each transaction.
A sequence of database requests that accesses the database. A _ is a logical unit of work; that is, it must be entirely completed or aborted—no intermediate ending states are accepted. All _ must have the properties of atomicity, consistency, isolation, and durability.
A feature used by the DBMS to keep track of all transaction operations that update the database. The information stored in this log is used by the DBMS for recovery purposes.
A set of rules that governs how transactions acquire and relinquish locks. _ locking guarantees serializability, but it does not prevent deadlocks. The _ protocol is divided into two phases:
(1) A growing phase occurs when the transaction acquires the locks it needs without unlocking any existing data locks. Once all locks have been acquired, the transaction is in its locked point.
(2) A shrinking phase occurs when the transaction releases all locks and cannot obtain a new lock.
When you are trying to achieve concurrency control, _ cause problems with data integrity and consistency. These problems occur when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the _, thus violating the isolation property of transactions.
In concurrency control, a property of timestamping that ensures no equal timestamp values can exist.
A concurrency control scheme in which an older transaction must wait for the younger transaction to complete and release the locks before requesting the locks itself. Otherwise, the newer transaction dies and is rescheduled.
A concurrency control scheme in which an older transaction can request the lock, preempt the younger transaction, and reschedule it. Otherwise, the newer transaction waits until the older transaction finishes.
In concurrency control, a process that ensures transaction logs are written to permanent storage before any database data are actually updated.
In concurrency control, a process that ensures a database is immediately updated by operations during the transaction's execution, even before the transaction reaches its commit point.