Wednesday, March 12, 2014

Storage types of cube MOLAP, ROLAP, HOLAP

A cube is a structure made of number of dimensions, measures, etc.
Cubes usually rely on two kind of tables like 'fact-table' (for cubes) & 'dimension-table' (for cube’s different dimensions).
A cube can have only one fact-table and ‘n’ number of dimension tables (based on no: of dimensions in the cube).
It store the data in pre-aggreagted form.

Cube Storage type:
MOLAP (Multi dimensional Online Analytical Processing)
MOLAP is the most used storage type. Its designed to offer maximum query performance to the users. Data AND aggregations are stored in optimized format in the cube. The data inside the cube will refresh only when the cube is processed, so latency is high.

ROLAP (Relational Online Analytical Processing)
ROLAP does not have the high latency disadvantage of MOLAP. With ROLAP, the data and aggregations are stored in relational format. This means that there will be zero latency between the relational source database and the cube. Disadvantage of this mode is the performance, this type gives the poorest query performance because no objects benefit from multi dimensional storage.

HOLAP (Hybrid Online Analytical Processing)
HOLAP is a storage type between MOLAP and ROLAP. Data will be stored in relational format(ROLAP), so there will also be zero latency with this storage type. Aggregations, on the other hand, are stored in multi dimensional format(MOLAP) in the cube to give better query performance. SSAS will listen to notifications from the source relational database, when changes are made, SSAS will get a notification
and will process the aggregations again.With this mode it’s possible to offer zero latency to the users but with medium query performance compared to MOLAP and ROLAP.

We use MOLAP storage type generally for deliver high performance

More clear image to understand the storage type of cubes:-

No comments:

Post a Comment

web stats