What is microsoft access database
With ODBC's in-memory policy, transactions also allow for many updates to a record to occur entirely within memory, with only one expensive disk write at the end. There is no chance that only some of the updates will end up written to the database either all will succeed, or the changes will be discarded when the database system restarts. Transactions also permit the state of the database to remain consistent if a system failure occurs in the middle of a sequence of updates required to be atomic. This is called rolling back the transaction, or just rollback, and it restores the state of the database records to precisely the state before the transaction began. One of the main advantages is that transactions can be abandoned if a problem occurs during the transaction. Transactions have a number of advantages over independent database updates. 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.
WHAT IS MICROSOFT ACCESS DATABASE SERIES
( ODBC systems have one-level transaction processing, while several ISAM systems like Paradox do not support transaction processing.) A transaction is a series of operations performed on a database that must be done together - this is known as atomicity and is one of the 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. 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.
WHAT IS MICROSOFT ACCESS DATABASE 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 locks one record, 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. 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 modify only those database records (that is, items in the database) to which the user has applied a lock, which gives 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 Indexed Sequential Access Method 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 a (random access) file system API.