Indexes

[Former Member]

Hi ,

Can anyone tell how Indexes in Cube work internally to improve performance ?

What is Primary and secondary Index ?

How many index we can create for Cube ?

Can we create index for ODS ?

Kumar

[Former Member · Accepted solution]

Hi dear,

look at

http://help.sap.com/saphelp_nw04/helpdata/en/80/1a6473e07211d2acb80000e829fbfe/frameset.htm

http://help.sap.com/saphelp_bw33/helpdata/en/4a/e71f39488fee0ce10000000a114084/frameset.htm

for more details...

Hope it helps!

Bye,

Roberto

[Former Member]

Hi Kumar,

A primary index is defined in terms of the primary key fields of a table. It is set up by the system (example: ODS index).

A secondary index is any additional index defined on any combination of other fields. This can be set by the user (example: ODS as from BW3.x).

In cubes, one speaks about bitmap indexes (more appropriate to the star schema).

Indexes are useful in combination with DB statistics.

It is interesting to create a secondary index on an ODS if one knows that a certain field or combination of fields will be used as a selection parameter of a query and if this can improve query execution performance (high volumes of data).

Dimension tables have an index built on the Dim ID and another built on the SID values of the characteristics in that dimension by the system automatically.

It can make sense in some cases to add an additional index(s) on the Dimension table to allow an indexed read in stead of a full table scan the could occur depending on the filterin done in the query. This decision is just like what you go thru when to decide to add a secondary index to an ODS.

It can also make sense to build an additional index on Master Data tables fo rthe same reasons.

Secondary indexes can be added to an ODS thru the BW Admin Workbench, but indices on Dim and Master Data tables can usually only be cuilt by your DBA.

Hope it helps.

Regards,