dbs/db4/qaqqinilib is a SAP Parameter attribute which is used to control Library that contains QAQQINI file information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
The so-called QAQQINI file can be used to influence optimizer behavior.
If this parameter is left blank, the system uses automatically the
system-wide file in QUSRSYS, if existing.
If you would like to make changes that should only affect this SAP
system, you would make them to a local copy of this file. This parameter
can then be used to specify the library in which you put the copy.
See SAP Notes 820325, 541508, 485420 for details, documentation, and
popular use cases.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.