Cost vs. advantage of moving from IMS DB to DB2

Well, the main advantages of converting from IMS/DB to DB2 would be the better support for ad hoc query, support of standard SQL (instead of non-standard DL/1) for writing queries and a deeper pool of talent to support the DB2 environment (there are more DB2 folks out there than IMS folks now-a-days).

The benefit of sticking with IMS is the good performance you currently enjoy as well as no need to convert the database structures or the 7 million lines of application code.

I guess it boils down to this: How happy are you with the current application, are you able to support it properly and how many other IMS/DB databases do you support? If this is the last IMS/DB database and you are looking to convert to rid yourself of the IMS license, then it might make sense to convert. But you should do a project plan and cost/benefit analysis before making your final decision (conversion can be very costly). If you have a lot of other IMS/DB databases, then don't convert to DB2 unless you cannot support the needs of your end users (management, ad hoc support, etc.) using IMS.

In terms of CPU requirements, DB2 will consume more CPU than IMS. DB2 optimizes queries internally whereas IMS programs construct access paths to data. This additional requirement will cause DB2 to consume more CPU.

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