rsdb/reco_sleep_time is a SAP Parameter attribute which is used to control Influence the Sleeptime between two DB-Reconnect Attempts 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 .
0 no wait time between the 'i' and (i+1) database reconnect attempt. n The wait time between 2 database reconnect attempts is n seconds. The maximum number of database reconnect attempts that can be executed depends on the setting of parameter
See SAP Parameter Documentation for full SAP documentation for this profile parameter.