Local Cube Size - Defining The Problem, Proposing A Solution

Thu, 17 May 2007 15:48:22 GMT

Local cube files can dramatically improve cube browsing speed performance - but only if they're small enough:

1. For Small Cubes - browsing the Analysis Server cube and browsing a local cube both have excellent performance - but the local cube will usually be faster.

2. For Medium Cubes - browsing the Analysis Server cube and browsing a local cube will both usually have excellent performance, but performance can slow when using low levels of large dimensions. The Analysis Server cube will often be faster.

3. For Large Cubes - browsing the Analysis Server cube is still very good, as long as the cubes are properly optimized, but performance can be slow when working with large levels. Large local cubes have poor performance and will sometimes lock up client tools. But this is where the use of local cubes can be extremely beneficial - if you can find a way to create a set of small, high performance local cube files that give the user the portions of the large Analysis Server cubes that they really need.

What size of local cubes am I talking about? The tipping point between Small, Medium, and Large cubes varies enormously depending on server capacity, local computer capacity, the specific OLAP client tool being used, and network performance. But, as a general rule, I would say:

1. Small Cubes (both perform well, local cubes are faster) - Under 10-25 MB local cube file size.

2. Medium Cubes (both perform well, Analysis Server cubes are faster) - 25-50 MB local cube file size.

3. Large Cubes (local cubes perform poorly or not al all - create subsets) - Over 50-100 MB local cube file size.

The Solution - Use local cube files - especially for your large cubes - but keep the local cube files small by including only a small portion of the server cube. How can you do that? Here are the most effective strategies:

1. Remove large dimensions.

2. Remove large lower levels of large dimensions. When you do this, make sure you move the dimension key to the higher level, so the low levels aren't included because they're needed to provide the connection to the fact table.

3. Remove less important attributes from large dimensions.

4. Include only a slice of the members of a large dimension.

5. Slice a different dimension in a way that eliminates most of the members of all the large dimensions. For example, for some businesses, including sales only for the current month will eliminate 95% of the customers in a large customer dimension.

All of these strategies are possible as a point-and-click solution when using CubeSlice. They're also possible, of course, by directly manipulating the ASSL script used to create a local cube file.

This is the most important topic in the creation of local cube files - and the most important topic for this blog. I'll be discussing the details of minimizing the size and optimizing the performance of local cube files in many future posts. For now, if you want more information, please look at my whitepaper and demo that show how this can be done:

How to Dramatically Improve Browsing Speed Performance for SQL Server 2005 Analysis Services

http://www.cubeslice.com/BrowsingPerformance.doc

Local Cube Performance Demo:

http://www.cubeslice.com/CubeSlice_Performance_Demo.exe

Feedback Please: What's your experience with the performance of different size local cube files?

An Introduction to Local Cube Files

Fri, 11 May 2007 18:32:37 GMT

DEFINITION

A local cube is a file that contains multidimensional (OLAP) data, which can be browsed in the same way as an Analysis Server cube.

EXTENSION

.cub

HISTORY

First appeared with Analysis Services in Microsoft SQL Server 7 and with Microsoft Excel in Office 2000. They received significant improvement with the release of Analysis Services in Microsoft SQL Server 2005.

LOCAL CUBE SIZE AND PERFORMANCE

As a general rule, a small local cube file will have faster browsing speed than the same Analysis Server cube, while a large local cube file will have slower browsing speed than the same Analysis Server cube.

Can we predict what size of local cube file will give excellent browsing performance?

Not exactly - but based on our experience we try to keep local cube files under 10 MB - and certainly under 25 MB.

If you have large Analysis Server cubes it's still good to use local cubes - in fact, it's even more important to use local cubes to get excellent perormance - but you're going to have to put only a portion of your server cube into your local cube.

The rule for local cubes and performance is to always try it and see how it works.

HOW TO CREATE

Microsoft Excel provides two wizards to create local cube files. One wizard is used when connected to an Excel Pivot Table and creates a local cube from an Analysis Server cube. The other wizard can be used to create a local cube from a relational database.

Our company, SDG Computing, Inc, first offered an automated local cube creation product, the Local Cube Task, in 2001. That product has now been converted into a product called CubeSlice.

Many other OLAP tool vendors have provided some support for creating local cube files. Most OLAP client tool vendors have provided support for browsing local cube files.

Microsoft has provided several ways to create a local cube programmatically as a part of their data access libraries:

CREATE LOCAL CUBE - Allows a user to create a local cube from either an Analysis Server cube or from a relational data source. First introduced with SQL Server 7. This command has reduced support and has been deprecated in SQL Server 2005.

CREATE GLOBAL CUBE - Allows a user to create a local cube from an Analysis Server cube. Introduced with SQL Server 2000.

ASSL (Analysis Services Scripting Language) CREATE - Allows a user to create a local cube from either an Analysis Server cube or a relational data source. Introduced with SQL Server 2005.

For more information on the different ways of programmatically creating local cubes, see: http://www.cubeslice.com/lcicdifferentwaystocreate.htm

Tim Peterson's BI Performance Blog: Performance and Local Cubes

Local Cube Size - Defining The Problem, Proposing A Solution

An Introduction to Local Cube Files