Advantages and disadvantages of ROLAP and molap

In OLAP technical documents, there are two main types that are often mentioned: multidimen1_olap (molap) and Relational OLAP (ROLAP). In order to combine the advantages, based on the two, a new type of Hybrid OLAP (holap) is proposed, that is, Hybrid OLAP technology. From a technical point of view, ROLAP (microstrategy implementation) and molap (COGNOS implementation) have their own advantages. The former is based on relational databases. Its OLAP engine converts user OLAP operations, such as drill-up and drill-down filtering and merging, into SQL statements, and submits them to the database for execution. It also provides the aggregation navigation function, locate the SQL query to the coarse-grained fact table based on the dimension and measurement of user operations. In contrast, molap calculates the summary data in advance and stores it in its own specific multi-dimensional database. Your OLAP operations can be directly mapped to multi-dimensional database access without SQL access. Therefore, the difference between the two is that ROLAP provides greater flexibility and molap provides a faster speed.

Molap

As the most commonly used OLAP analysis method, in molap, data is stored in multi-dimensional cubes, and the multi-dimensional data is organized as the core. That is to say, molap uses multi-dimensional arrays to store data. Multi-dimensional data will form a "cube" structure in storage, in molap, "rotation", "cut", and "slice" of "cube" are the main technologies used to generate multidimensional data reports.

Advantages:

Superior performance:Molap cube provides fast data retrieval and query, and provides the best operations such as slicing, rotating, and partitioning.

Complex computing:All calculations in molap are processed in advance when the cube is generated. Therefore, molap is not only capable of complex computing, but also fast.

Disadvantages:

Only limited data can be processed:Because all computations are processed when the cube is generated, it is impossible to contain a large amount of data in the cube. However, this means that the data in the cube cannot process a large amount of data, you cannot include all the data in the cube. However, due to this restriction, only the information of the summary-level (Summary class) can be included in the cube.

Additional investment required:Because cube technology is usually private, using molap may increase costs such as human resources and finance.

ROLAP

This method relies on the relational database engine to provide functions such as slicing, drill-Up, And drill-down. Each slice or drill-up operation is converted into an SQL statement and submitted to the database for execution.

Advantages:

It can process a large amount of data:Because ROLAP technology depends on relational databases, its data is stored in relational databases, so it does not have restrictions on data storage space.

You can use relational database functions:Because ROLAP technology is built on relational databases, it can easily use these functions.

Disadvantage:

Low performance:Because the nature of ROLAP technology is to perform SQL queries or multiple SQL queries in relational databases, it may be slow to return results when the data volume is large.

QuiltSQLRestrictions:Because ROLAP technology relies mainly on generating SQL statements for query implementation in relational databases, SQL statements are not suitable for such requirements. For example, it is difficult to use SQL statements for summary calculation.

Holap

Holap technology combines the advantages of molap and ROLAP technologies. For summary data, holap uses cube technology to provide faster performance. When a large amount of detailed information needs to be queried, holap can "drill through" the cube to access the relevant data under the cube.