Understanding Wide-Column Stores

To understand the concept  more clearly, let’s start with an example of Relational database:

Customers
Id
Product
FN
Date
Country
1
Dell
Harry
17/04/2018
India
2
Dell
Harry
17/04/2018
India
3
Apple
Ron
17/04/2018
India
4
Sony
Ron
17/04/2018
South Africa
5
Sony
Hermione
17/04/2018
South Africa

When we convert this to a Column Store, this is how it looks like:
FN
LN
Product
Date
Country
Id
Value
Id
Value
Id
Value
Id
Value
Id
Value
1-2
Harry
1-2
Potter
1-2
Dell
1-5
17/04/2018
1-3
India
3-4
Ron
3-4
Weasley
3
Apple
4-5
South Africa
5
Hermione
5
Granger
4-5
Sony

Now a Wide Column store will Group the columns which are accessed frequently together into one , like

Id
Name
1-2
FN
Harry
LN
Potter
3-4
FN
Ron
LN
Weasley
5
FN
Hermione
LN
Granger

Some key points are,

  • Columns are created for each row rather than being predefined by the table structure. So, each row can have different columns.
  • We can thing of wide columns as a key-value collection, where each value in the collection is either a simple data type or another key-value collection.
  • In most systems, a third piece of data is usually held for each column: a timestamp that records when the data was added to the database or last modified. In above example, there would be one more column along with FN and LN to store timestamp.
  • Unlike traditional databases, a column in a wide-column database is not something that you define in advance – they are created as needed when sending data to the database.
The advantage of this design is processing power and ability to work with truly massive data sets.
Two most popular NoSQL wide-column databases are Cassandra, HBase and Amazon SimpleDB.

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