regarding indexes

Former Member — Sat, 23 Feb 2008 11:14:47 GMT

any documentation regarding indexes

primary index

secondery index

Re: regarding indexes

Former Member — Sat, 23 Feb 2008 11:17:51 GMT

Primary and secondary indexes

Index: Technical key of a database table.

Primary index: The primary index contains the key fields of the table and a pointer to the non-key fields of the table. The primary index is created automatically when the table is created in the database.

Secondary index: Additional indexes could be created considering the most frequently accessed dimensions of the table.

Structure of an Index

An index can be used to speed up the selection of data records from a table.

An index can be considered to be a copy of a database table reduced to certain fields. The data is stored in sorted form in this copy. This sorting permits fast access to the records of the table (for example using a binary search). Not all of the fields of the table are contained in the index. The index also contains a pointer from the index entry to the corresponding table entry to permit all the field contents to be read.

When creating indexes, please note that:

An index can only be used up to the last specified field in the selection! The fields which are specified in the WHERE clause for a large number of selections should be in the first position.

Only those fields whose values significantly restrict the amount of data are meaningful in an index.

When you change a data record of a table, you must adjust the index sorting. Tables whose contents are frequently changed therefore should not have too many indexes.

Make sure that the indexes on a table are as disjunctive as possible.

(That is they should contain as few fields in common as possible. If two indexes on a table have a large number of common fields, this could make it more difficult for the optimizer to choose the most selective index.)

Accessing tables using Indexes

The database optimizer decides which index on the table should be used by the database to access data records.

You must distinguish between the primary index and secondary indexes of a table. The primary index contains the key fields of the table. The primary index is automatically created in the database when the table is activated. If a large table is frequently accessed such that it is not possible to apply primary index sorting, you should create secondary indexes for the table.

The indexes on a table have a three-character index ID. '0' is reserved for the primary index. Customers can create their own indexes on SAP tables; their IDs must begin with Y or Z.

If the index fields have key function, i.e. they already uniquely identify each record of the table, an index can be called a unique index. This ensures that there are no duplicate index fields in the database.

When you define a secondary index in the ABAP Dictionary, you can specify whether it should be created on the database when it is activated. Some indexes only result in a gain in performance for certain database systems. You can therefore specify a list of database systems when you define an index. The index is then only created on the specified database systems when activated

Re: regarding indexes

Former Member — Sat, 23 Feb 2008 11:25:44 GMT

Primary Indexes :

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).

Secondary 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).

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

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).

Check out these links for Indexes :

https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/cccad390-0201-0010-5093-fd9ec8157802

https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/ce7fb368-0601-0010-64ba-fadc985a1f94

https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/4c0ab590-0201-0010-bd9a-8332d8b4f09c

https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/1955ba90-0201-0010-d3aa-8b2a4ef6bbb2

Thanks,

Sakthi C

Rewards if useful*

topic regarding indexes in Application Development and Automation Discussions

regarding indexes

Re: regarding indexes

Re: regarding indexes