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Sharding does destroy your relational database - which is a good thing. The idea behind sharding is to distribute data to several databases based on certain criterias. This could for example be the primary key. All entities that keys begin with 1 go to one database, with 2 to another and so on (often modulo functions on the key are used, or groups based on business data like customer location, or function). Several reasons exists for sharding, the main two being better performance and lower impact of crashed databases - only persons with a name that starts with S will be affected by a database crash.