I am converting my applications from VSAM to DB2. What kind of increases in CPU/other system resources, and decrease in application response times can I expect?
This is an impossible question to answer with any degree of accuracy. However, there is a boatload of advice I can give you. First of all, do not simply convert the data structures from VSAM to DB2 and leave the programs un-touched. A VSAM program and a DB2 SQL program are two different things and should not be coded in the same way. VSAM does record at a time processing; DB2 SQL does set at a time processing. An efficient VSAM program will likely become inefficient if converted to DB2 without taking this big difference into consideration.
DB2 queries will perform better when the filtering is done in the query. This means coding SQL statements using WHERE clauses to specify exactly what data is required. VSAM reads are frequently done by reading the data and then checking it to see if fields in the retrieved record match what the program is looking for. Though possibly efficient for VSAM this will kill DB2 performance.
Also, be sure to train your developers in SQL and your DBAs in relational database design, as well as in the technical aspects of DB2. Without this level of expertise you are sure to create inefficient DB2 databases and applications.
To finish, simply installing DB2 will not cause horrible performance problems and CPU spikes as you seem to be anticipating. Using DB2 improperly, though, will decidedly cause such problems. Good luck!
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