What are the concept of the data redundancy in database?Is redundancy in database is duplication of data in DB?
It is difficult to discuss data redundancy without some context, this topic comes up several times, and each time the objective is different. e.g.
if you are normalizing database schema the objective is to avoid storing data repeatedly, and thus the objective is to avoid data redundancy.
When we are studying Durability, we need to make sure we have some way of recovering from a failure(hardware / software), in this context we prepare to take backups of the database regularly by duplicating data on several different mediums, here the objective is to store data redundantly.
When we study redundancy in the context of database tuning, what we are trying to achieve is better performance. When each data item is stored exactly once in the database, we may need to show several data items together to the user by writing a join query which may contain several joins / tables. Such complex queries require more resources and more response time. To increase performance we duplicate some data items so as to avoid join query.
if you are normalizing database schema the objective is to avoid storing data repeatedly, and thus the objective is to avoid data redundancy.
When we are studying Durability, we need to make sure we have some way of recovering from a failure(hardware / software), in this context we prepare to take backups of the database regularly by duplicating data on several different mediums, here the objective is to store data redundantly.
When we study redundancy in the context of database tuning, what we are trying to achieve is better performance. When each data item is stored exactly once in the database, we may need to show several data items together to the user by writing a join query which may contain several joins / tables. Such complex queries require more resources and more response time. To increase performance we duplicate some data items so as to avoid join query.
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