What Is Persistent Data?
Computers and storage devices are full of data, and there are many different forms of data, depending on how often the data are accessed or modified. Persistent data are those that are typically not accessed and rarely modified. Database persistent data are typically stored on a server and are more commonly accessed than archived data. With archived data, or those stored on disks or tapes, the information is very rarely opened or used. Aside from archiving the data, this allows researchers to go through old or stored information to find past trends that may apply to present situations.
Persistent data are very rarely modified; this means the information stored within the database, disk or tape is not changed, except for special occasions. The information being accessed is more common than the information being modified, but it is still rarely done. These data also exist from one session to the next, unlike data types that only exist for one session and are then discarded or bound to that single session.
With database persistent data, an entire database or a section of a database is created to hold the archived data. This can be done locally, on a database stored on the computer’s hard drive, or it can be placed on a server. This persistent information is more commonly accessed than the tape and disk variant, because the information is readily available. At the same time, this database will typically exist untouched for months or years.
Tape and disk persistent data are not meant to be touched, or even loaded into a computer, for years. These data are meant strictly for archival purposes and are very rarely accessed at all. Persistent information is often large, so it is commonly erased from the local hard drive once the information is archived, so the tape or disk is usually the only copy of the data.
There are several reasons why a developer or administrator would want to archive persistent data. While the information may not be current or presently useful, the data may be useful later to researchers, or they may be useful in finding a trend based on old information. Another reason is to reduce digital clutter from the hard drive. Hard drives need space to function, and large chunks of persistent data can easily take up an entire hard drive. To avoid a full hard drive, the administrator will archive the unused data.
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