Replication (computing)

In computer science, replication refers to the provision of redundant resources (software or hardware components) to improve reliability and fault-tolerance. Dynamic replication of data can also be used to improve performance. (See US Patent # 4432057). This applies especially in a multiplicity of computer systems (multiprocessors). Storage or backup of the same data on multiple file systems exemplifies replication. Database replication can take place, for example, in PostgreSQL, usually with a master/slave relationship between the original and the copy. The master logs the updates, which then ripple through to the slave. The slave outputs a message stating that it has received the update successfully, thus allowing the sending (and potentially re-sending until successfully applied) of subsequent updates. See also Coda and RAID. Multimaster replication, where updates can be submitted to any location, and then "ripple" through to other servers, is often desired, but introduces substantially increased costs and complexity which may make it unusable.

Another example of using replication appears in distributed shared memory systems, where it may happen that many nodes of the system share the same page of the memory - which usually means, that each node has a separate copy (replica) of this page.