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HANA Row vs Column storage? Columnar Dictionary Compression & Inverted index?

Row store is is best for :

  •  Table mainly contains distinct values
  •  Low compression rate
  •  All columns of are relevant
  •  No aggregation or search on non-indexed columns
  •  Table is fully buffered
  •  Table has a minor number of records
  •  Table contains unstructured data

Column store is best for :

  •  Column based operations on large number of rows
  •  Large number of columns, many unused
  •  Aggregations and intensive search
  •  Master and transactional data

Columnar Dictionary Compression

First the Column “Country” is sorted alphabetically like Belgium,Denmark,France, Italy, Spain as shown below. Since the Logical Table has 8 entries in total ie from Order 456 to Order 463 as shown below.

So as per below Column compression diagram we will have the entries like France  ( index 3 of Dictionary diagram ) is on 1st index of the Compressed column diagram , similarly Denmark ( index 2 of Dictionary diagram)  is on 5th index of the Compressed column diagram etc.

Inverted Index

Here after the Compressed Column, for the Inverted Index we have 5 entries as shown in the Diagram just like Dictionary Diagram . Here as per Dictionary Diagram Belgium comes at 7th position of the logical table, similarly Denmark comes twice in the logical table at 5,6 positions and so on.

 

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