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

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

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

Table 1 :

Row store corresponding to above table is

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

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Data Compression : SAP HANA provide series of data compression technique that can be used for data in the column store. To store the 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.

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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

Dictionary vector : Location

Dictionary vector : Gender

Now the Attribute vector corresponding to the above table 2 would be as follows. Here it stores the integer values , which is the positions in dictionary vector.

So the column store for above mentioned table 2 can be converted as combination of Dictionary and attribute vectors.

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