Database: Difference between revisions

Revision as of 18:30, 3 February 2012

Revision as of 20:47, 5 February 2012

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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 [[CPU cache|processor's [[cachecaches]]s. ThisThese 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.