rsdb/otr/mutex_n is a SAP Parameter attribute which is used to control Number of mutexes in Online Text Repository Buffer 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 .
Specifies the number of mutexes that are used for synchronization in the
Online Text Repository buffer. If the value is too small, the level of
parallelism can drop. If the value is too high, too much memory space is
used. If the value is zero, a value is chosen that allows the greatest
possible level of parallelism (with an increased memory requirement).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.