SAP HANA : The Row store , column store and Data Compression

[former_member216493]

Here is an attempt to explain the row store data layout, column store data layout and the data compression technique.

Row Store : Here all data connect to a row is placed next to each other. See below an example.

Table 1 :

Name	Location	Gender
…..	…..	….
Sachin	Mumbai	M
Sania	Hyderabad	F
Dravid	Bangalore	M
…….	……	……

Row store corresponding to above table is

Column store : Here contents of a column are placed next to each other. See below illustration of table 1.

Data Compression : SAP HANA provide series of data compression technique that can be used for data in the column store. To store contents of a column , the HANA database creates minimum two data structures. A dictionary vector and an attribute vector. See below table 2 and the corresponding column store.

Table 2.

Record	Name	Location	Gender
…..	…..	…..	….
3	Blue	Mumbai	M
4	Blue	Bangalore	M
5	Green	Chennai	F
6	Red	Mumbai	M
7	Red	Bangalore	F
……	…..	……	……

Here in the above example the column ‘Name’ has repeating values ‘Blue’ and ‘Red’. Similarly for ‘Location’ and ‘Gender’. The dictionary vector stores each value of  a column only once in a sorted order and also a position is maintained against each value. With reference to the above example , the dictionary vectors of Name , Location and Gender could be as follows.

Dictionary vector : Name

Name	Position
….	……
Blue	10
Green	11
Red	12
…..	……

Dictionary vector : Location

Location	Position
….	……
Bangalore	3
Chennai	4
Mumbai	5
…..	……

Dictionary vector : Gender

Gender	Position
F	1
M	2

Now the Attribute vector corresponding the above table would be as follows. Here it stores the integer values , which is the positions in dictionary vector.