rdisp/PG_FAST_REL is a SAP Parameter attribute which is used to control 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 .
This parameter describes whether the administration of the paging blocks
is to work with a session-specific concatenation. This means that
operations, such as releasing blocks, can be executed more quickly.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.