Dim number and performance

[Former Member]

Hi gurus!

i've heard that when number of dimensions in one app exceeds 12 or 13(can't remember the exact number) there is a huge performance decrease,so we have to try to maintain dim number <13 .

Is that true?

[former_member200327 · Accepted solution]

The magic number could be13 - this is the number after which Full optimization starts making sense.

This based on a rule that BW can have only 13 user defined table Dimensions, so when BPC App has more than 13 Dimensions system combines some of them together to comply with that "13" rule. Initially it doesn't know what Dimensions to put together, but when you run Full optimization it moves together those Dimensions that produce less combination in Fact table. When you add more data you can run Full again and it can adjust Fact table.

So, if all you Dimensions are completely independent and Fact table contains almost all combinations of those, than yes - more than 13 will affect App performance. But is some of you Dimensions are dependent, so only few combinations can occur in Transaction data then more than 13 Dimensions should not affect much performance.

Hope this explains some of the logic behind it.

Gersh

[Former Member]

Hi,

great informations about performance. Thank you.

Another question about performances: what is the impact of the number of hierarchies per dimension?

regards,

Alex

[Former Member]

Wow, thank you very much for such detailed info!

the only question-what do you mean saying "independent/dependend dimensions"?

Thanks!

Edited by: susersuser on Mar 31, 2011 9:16 AM

[former_member200327]

An example of dependent Dimensions would be Cost Center and Entity - not all combinations make sense.

An example of independent Dimensions would be Entity and Time - most of the combinations make sense.

Hope this makes soem sense:).

Gersh

[Former Member]

It makes perfect sense.

Thank you very much!

[Former Member]

Hi,

As per the SAP's training guide, you can keep it till 20. But beyond that, the performance will degrade.