CODEWITHSUNDEEP
olap
user284291
user284291

Reputation:

What is use of OLAP?

How is it that OLAP data access can be faster than OLTP?

Upvotes: 1

Views: 9637

Answers (3)

Lynn Langit
Lynn Langit

Reputation: 4060

OLAP is fundamentally for read-only data stores. Classic OLAP is a Data Warehouse or Data Mart and we work with either as an OLAP cube. Conceptually you can think of an OLAP Cube like a huge Excel PivotTable. That is a structure with sides (dimensions) and data intersections (facts) that has NO JOINS.

The data structure is one of the reasons that OLAP is so much faster to query than OLTP. Another reason is the concept of aggregations, which are stored intersections at a level higher the leaf (bottom). An example would be as follows:

You may load a cube with the facts about sales (i.e. how much in dollars, how many in units, etc..) with one row (or fact) for each sales amount by the following dimensions - time, products, customers, etc..The level at which you load each dimension, for example sales by EACH day and by EACH customer, etc...is the leaf data. Of course you will often want to query aggregated values, that is sales by MONTH, by customers in a certain CITY, etc...

Those aggregations can be calculated at query time, or they can be pre-aggregated and stored at cube load. At query time, OLAP cubes use a combination of stored and calculated aggregations. Unlike OLTP indexes, PARTIAL aggregations can be used.

In addition to this, most OLAP cubes have extensive caching set up by default and most also allow for very granular cache tuning (pre-loading).

Another consideration is that relatively recently in-memory BI (or OLAP) is being offered by more and more vendors. Obviously, if more of the OLAP data is in memory, then resulting queries will be EVEN faster than traditional OLAP. To see an example of an in-memory cube, take a look at my slide deck about SQL Server 2012 BISM.

Upvotes: 6

Andrew Bezzub
Andrew Bezzub

Reputation: 16032

OLAP makes data access very quick by using of multidimensional data model. If you have huge amount of data and report generation is extremely long (e.g. several hours) you could use OLAP to prepare the report. Then each request to already processed data would be fast.

Upvotes: 6

ca8msm
ca8msm

Reputation: 1220

You need to do some research on what OLAP is and why/when you need to use it. Try starting by searching Google for OLAP, and read this wikipedia article:

http://en.wikipedia.org/wiki/Online_analytical_processing

Upvotes: 1

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