Shard (database architecture)

EN Texte en anglais Pas encore d'article dans ta langue : extrait en anglais.

A database shard, or simply a shard, is a horizontal partition of data within a database or search engine. Each shard may be held on a separate database server instance in order to spread across multiple servers. Some data in a database may remain present in all shards, while other data is stored in only one shard. In such cases, each shard acts as the single source for its subset of data. Horizontal partitioning is a database design principle whereby rows of a database table are held separately, rather than being split into columns (as in normalization and vertical partitioning, to varying degrees). Each partition forms part of a shard, which may in turn be located on a separate database server or in a separate physical location. There are numerous advantages to the horizontal partitioning of data. Since tables are divided and distributed into multiple servers, the total number of rows in each table in each database is reduced. This reduces index size, which generally improves search performance. A database shard can be placed on separate hardware, and multiple shards can be placed on multiple machines.