Index Tables to avoid BSEG fetching

Many times we have seen many threads related to performance issues on BSEG table. It takes quite a lot of time when fetching data directly from BSEG if we do not have proper key fields. Here is the solution for this. Since it is not possible to create the secondary INDEX for cluster tables, SAP came up with new concept called INDEX tables.

All the accounting documents (Open and closed) are stored in BKPF and BSEG tables and querying these tables takes lot of time. So SAP has created INDEX tables for BSEG which are updated with specific data based on classification and are much faster than BSEG.

EG: Customer documents, Vendor documents etc.

Index Tables:

BSID- Accounting: Secondary Index for Customers (Open Items)
BSAD- Accounting: Secondary Index for Customers (Cleared Items)
BSIK- Accounting: Secondary Index for Vendors (Open Items)
BSAK- Accounting: Secondary Index for Vendors (Cleared Items)
BSIS- Accounting: Secondary Index for G/L Accounts (Open Items)
BSAS- Accounting: Secondary Index for G/L Accounts (Cleared Item)

How to remember these tables???
Remember BS*  *

3^rd letter indicates whether item is open or closed.
I - For open items.
A-    For closed items.

4^th letter indicates classification. 
     D- For customers
     K- For vendors
     S- For G/L accounts.

These tables are some examples which is mostly required in real time scenarios. There are few more INDEX tables like this.