Database: Difference between revisions

Revision as of 20:15, 1 February 2012

Revision as of 18:30, 3 February 2012

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{{Main|Parallel database}}

::A '''parallel database''', run by a parallel DBMS, seeks to improve performance through [[Parallel computing|parallelization]] for tasks such as loading data, building indexes and evaluating queries. Parallel databases improve processing and [[input/output]] speeds by using multiple [[central processing unit]]s (CPUs) (including [[multi-core processor]]s) and [[DataComputer data storage|storage]] in parallel. In parallel processing, many operations are performed simultaneously, as opposed to serial, sequential processing, where operations are performed with no time overlap.

::The major parallel DBMS architectures (which are induced by the underlying [[Computer hardware|hardware]] architecture are:

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:See also ''[[Data migration#Database migration|Database migration]]'' in ''[[Data migration]]''

A database built with one DBMS is not [[Software portability|portable]] to another DBMS (i.e., the other DBMS cannot run it). However, in some situations it is desirable to move, migrate a database from one DBMS to another. The reasons are primarily economical (different DBMSs may have different [[Total cost of ownership|total costs of ownership]]-TCO), functional, and operational (different DBMSs may have different capabilities). The migration involves the database's transformation from one DBMS type to another. The transformation should maintain (if possible) the database related application (i.e., all related application programs) intact. Thus, the database's conceptual and external architectural levels should be maintained in the transformation. It may be desired that also some aspects of the architecture internal level are maintained. A complex or large database migration may be a complicated and costly (one-time) project by itself, which should be factored into the decision to migrate. This in spite of the fact that tools may exist to help migration between specific DBMS. Typically a DBMS vendor provides tools to help importing databases from other popular DBMSs.

==Implementation: Database management systems==

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More examples of storage types:

*Volatile storage can be found in processors, computer memory (e.g., DRAM), etc.

*Non-volatile storage types include [[Read-only memory|ROM]], [[EPROM]], [[Hard disk drive]]s, [[Flash memory]] and [[Flash drive|drivesdrive]]s{{dn|date=February 2012}}, [[Storage array]]s, etc.

=====Storage metrics=====

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=====Database storage hierarchy=====

A database, while in operation, resides simultaneously in several types of storage. By the nature of contemporary computers most of the database part inside a computer that hosts the DBMS resides (partially replicated) in volatile storage. Data (pieces of the database) that are being processed/manipulated reside inside a processor, possibly in processor's [[cache]]s. This data are being read from/written to memory, typically through a computer [[Bus (computing)|bus]] (so far typically volatile storage components). Computer memory is communicating data (transferred to/from) external storage, typically through [[standard]] storage interfaces or networks (e.g., [[fibre channel]], [[iSCSI]]). A [[Disk array|storage array]], a common external storage unit, typically has storage hierarchy of it own, from a fast cache, typically consisting of (volatile and fast) [[DRAM]], which is connected (again via standard interfaces) to drives, possibly with different speeds, like [[flash drive]]s{{dn|date=February 2012}} and magnetic [[disk drive]]s (non-volatile). The drives may be connected to [[magnetic tape]]s, on which typically the least active parts of a large database may reside, or database backup generations.

Typically a correlation exists currently between storage speed and price, while the faster storage is typically volatile.