There are three standard storage modes in OLAP applications.
When ever the cube process is going on then it process leaf level data(detailed data) and creates Aggregations based on the Aggregation design defined in the cube. Now lets see about these in detail –
MOLAP – Stores Detailed data and Aggregations in the form of binary files and these are completely separate from relational database.
ROLAP – Stores Detailed data and Aggregations in the relational database.
HOLAP – Stores Detailed data in relational database and Aggregations in the form of binary files.
PFB the difference between these three –
|Storage Mode||Storage Location for Detail Data||Storage Location for Summary/ Aggregations||Storage space requirement||Query Response Time||Processing Time||Latency|
|MOLAP||Multidimensional Format||Multidimensional Format||MediumBecause detail data is stored in compressed format.||Fast||Fast||High|
|HOLAP||Relational Database||Multidimensional Format||Small||Fast for aggregated data and Slow when trying to read Leaf level data.||Fast||Medium|
|ROLAP||Relational Database||Relational Database||Large||Slow||Slow||Low|
There is one main difference between ROLAP and MOLAP i.e ROLAP supports REAL TIME Data where as MOLAP doesn’t. Real time in the sense when a record is inserted into fact table then it should be immediately available for analysis. It doesnot happen if you use MOLAP storage mode and to pull newly added record in MOLAP storage mode we need to process cube. In ROLAP as the data is storing in relational databases, when ever a record is inserted into table it will be available for analysis.
Roopesh Babu V