Point-in-time Consistency
Data is point-in-time consistent if all of the interrelated data components (either a group of data sets or a set of logical volumes) are as they were at any single instant in time.
Point-in-time consistency is an important property of backup files and a critical objective of software that creates backups. It is also relevant to the design of disk memory systems, specifically relating to what happens when they are unexpectedly shut down.
As a relevant backup example, consider a website with a database such as the online encyclopedia Wikipedia, which needs to be operational around the clock, but also must be backed up with regularity to protect against disaster. Portions of Wikipedia are constantly being updated every minute of every day, meanwhile, Wikipedia's database is stored on servers in the form of one or several very large files which require minutes or hours to back up.
These large files - as with any database - contain numerous data structures which reference each other by location. For example, some structures are indexes which permit the database subsystem to quickly find search results. If the data structures cease to reference each other properly, then the database can be said to be corrupted.
Read more about this topic: Data Consistency
Famous quotes containing the word consistency:
“People who love only once in their lives are ... shallow people. What they call their loyalty, and their fidelity, I call either the lethargy of custom or their lack of imagination. Faithfulness is to the emotional life what consistency is to the life of the intellect—simply a confession of failures.”
—Oscar Wilde (1854–1900)