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About your query on dropping Vanilla Index, please note that any manual modifications performed directly at database layer on the physical database schema are not supported.
So to summaries:
Custom Index :
1. You may create and drop indexes and you can refer this to your developers.
2. Dropping indexes may impact to Application performance in the future
1. Its not advice able to drop Vanilla Indexes as this will cause the Siebel Application in a UN-supported mode
2. If you wish to do, you may engage the Expert Service( Billable) for more details.
I hope it helps.
Yeah article applies to DB2 z/OS only.
Expert services will analyse the situation and if that part of functionality or piece of application is not using that index and if does not has overall impact on application, they may give you green signal after through analysis.
Since proactive analysis is something support does not do, we normally recommend to have someone who can physically analyse the situation and apply the requirement from client and expert services are better candidates for them.
I hope it helps you.