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What is denormalization and when would you go for it?
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Answer Posted / sandeepa rout
De-normalization is the process of attempting to optimize
the performance of a database by adding redundant data. It
is sometimes necessary because current DBMSs implement the
relational model poorly.
Only one valid reason exists for denormalizing a relational
design - to enhance performance. However, there are several
indicators which will help to identify systems and tables
which are potential denormalization candidates. These are:
* Many critical queries and reports exist which rely upon
data from more than one table. Often times these requests
need to be processed in an on-line environment.
* Repeating groups exist which need to be processed in a
group instead of individually.
* Many calculations need to be applied to one or many
columns before queries can be successfully answered.
* Tables need to be accessed in different ways by different
users during the same timeframe.
* Many large primary keys exist which are clumsy to query
and consume a large amount of DASD when carried as foreign
key columns in related tables.
* Certain columns are queried a large percentage of the
time. Consider 60% or greater to be a cautionary number
flagging denormalization as an option.
| Is This Answer Correct ? | 18 Yes | 5 No |
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