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SQL refers to Structured Query Language, a kind of language used to access, update and manipulate database. In SQL, ROLLBACK is a command that causes all data changes since the last START TRANSACTION or BEGIN to be discarded by the relational database management systems (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.
TRANSACTION START; TRANSACTION COMMIT (exceptions raised here prevent the transaction from committing, or preparing if a two-phase commit is involved) TRANSACTION ROLLBACK; Database-level triggers can help enforce multi-table constraints, or emulate materialized views. If an exception is raised in a TRANSACTION COMMIT trigger, the changes made ...
Cascading aborts occur when one transaction's abort causes another transaction to abort because it read and relied on the first transaction's changes to an object. A dirty read occurs when a transaction reads data from uncommitted write in another transaction. [9] The following examples are the same as the ones in the discussion on recoverable:
Each transaction may consist of several individual operations yet, as a whole, it moves the system between consistent states. There are two groups of systems where compensating transaction may be applied: 1. In the context of a database this is often easily achieved using transactions and the commit/rollback mechanism. [1]
Optimistic concurrency control transactions involve these phases: [2] Begin: Record a timestamp marking the transaction's beginning. Modify: Read database values, and tentatively write changes. Validate: Check whether other transactions have modified data that this transaction has used (read or written). This includes transactions that ...
A database transaction symbolizes a unit of work, performed within a database management system (or similar system) against a database, that is treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:
A savepoint is a way of implementing subtransactions (also known as nested transactions) within a relational database management system by indicating a point within a transaction that can be "rolled back to" without affecting any work done in the transaction before the savepoint was created. Multiple savepoints can exist within a single ...
Cursors are usually closed automatically at the end of a transaction, i.e. when a COMMIT or ROLLBACK (or an implicit termination of the transaction) occurs. That behavior can be changed if the cursor is declared using the WITH HOLD clause (the default is WITHOUT HOLD).