- MICROSOFT ACCESS DATABASE ENGINE 2007 UPDATE
- MICROSOFT ACCESS DATABASE ENGINE 2007 SERIES
- MICROSOFT ACCESS DATABASE ENGINE 2007 WINDOWS
Until the transaction is committed, changes are made only in memory and not actually written to disk. For transaction processing to work (until Jet 3.0), the programmer needed to begin the transaction manually, perform the operations needed to be performed in the transaction, and then commit (save) the transaction.
MICROSOFT ACCESS DATABASE ENGINE 2007 SERIES
A transaction is a series of operations performed on a database that must be done together - this is known as atomicity and is a part of ACID (Atomicity, Consistency, Isolation, and Durability), concepts considered to be the key transaction processing features of a database management system. Jet supports transaction processing for database systems that have this capability ( ODBC systems have one level transaction processing, while several ISAM systems like Paradox do not have transaction processing capability). Lock conflicts, which either require the user to wait, or cause the request to fail (usually after a timeout) are more common with pessimistic locking. Other users must wait until the lock is released in order to make their changes.
MICROSOFT ACCESS DATABASE ENGINE 2007 UPDATE
With pessimistic locking, the update is guaranteed to succeed once the lock is obtained. However, with optimistic locking one cannot be certain that the update will succeed because another user could lock the record first. Conflicts are less likely to occur with optimistic locking, since the record is locked only for a short period of time. With pessimistic locking, the record or page is locked immediately when the lock is requested, while with optimistic locking, the locking is delayed until the edited record is saved. There are two mechanisms that Microsoft uses for locking: pessimistic locking, and optimistic locking. In Jet 4, the record locking model eliminates collateral locks, so that every record that is not in use is available. As a result, no other user can access the collaterally locked records, even though no user is accessing them and there is no need for them to be locked. The page locking model works by locking the pages, instead of individual records, which though less resource intensive also means that when a user intentionally locks one record, any and all other records on the same page are collaterally locked. Data is stored in "records" of variable length that may take up less or more than one page. Microsoft databases are organized into data "pages", which are fixed length (2 kB before Jet 4, 4 kB in Jet 4) data structures that divide up the database. In Jet versions before version 4, a page locking model is used, and in Jet 4, a record locking model is employed. Any single user can only modify those database records (that is, items in the database) to which they have applied a lock that gives them exclusive access to the record until the lock is released. To prevent that data from being corrupted or invalidated when multiple users try to edit the same record or page of the database, Jet employs a locking policy. Jet allows multiple users to access the database concurrently. DAO provides an API that allows programmers to access JET databases using any programming language. The final module is the Data Access Objects (DAO) DLL. Another one of the modules contains the ISAM Drivers, DLLs that allow access to a variety of ISAM databases, among them Xbase, Paradox, Btrieve and FoxPro, depending on the version of Jet. There are three modules to Jet: One is the Native Jet ISAM Driver, a dynamic link library (DLL) that can directly manipulate Microsoft Access database files (MDB) using Indexed Sequential Access Method (ISAM). Over the years, Jet has become almost synonymous with Microsoft Access, to the extent where many people refer to a Jet database as an "Access database". For larger database needs, Jet databases can be upgraded (or, in Microsoft parlance, "up-sized") to Microsoft's flagship database product, SQL Server.
MICROSOFT ACCESS DATABASE ENGINE 2007 WINDOWS
Jet is now part of Microsoft Windows and is no longer a component of Microsoft Data Access Components (MDAC). It has since been superseded for general use, however, first by Microsoft Desktop Engine (MSDE), then later by SQL Server Express. Microsoft Access and Visual Basic use or have used Jet as their underlying database engine. JET stands for Joint Engine Technology, sometimes being referred to as Microsoft JET Engine or simply Jet. The first version of Jet was developed in 1992, consisting of three modules which could be used to manipulate a database. A database engine is the underlying component of a database, a collection of information stored on a computer in a systematic way. The Microsoft Jet Database Engine is a database engine on which several Microsoft products have been built.
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