Isolation level

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Isolation level

Isolation level is a characteristic of a transaction and it mandates how one transaction must interact with other transactions accessing the same database, in terms of visibility and locking. There are three levels commonly used: Dirty Read, Read Committed and Repeatable Read. The first is the only mode in Paradox and it's supported by a few RDBMS products. The second is the default for almost any relational engine. The third is the default for Firebird/InterBase and it's done without bringing the engine to its knees (not the case with other engines). In addition, InterBase offers a higher level, known as Repeatable Read with Stability that can be used for special and short transactions. Thanks to the multi version capability, InterBase also allows explicit control over locking management (avoid, wait or give an error) that doesn't have sense on other "classic" engines.

Source: http://www.cvalde.net/document/glossary.htm

See also:
Firebird for the database expert: episode 5 - Locking and record versions
Transaction
TID
Isolation mode

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