Here are the sections of this Redbook: [NPGTHRSH] specifies whether Db2 is to use special access path selection for tables under a given size. Unless you use SAP, the default value is 0, which means that no special access path selection is used.

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  • http://ibmsystemsmag.com/blogs/db2utor/may-2018/ibm-redbook-db2-12-for-z-optimizer/