stat/bufsize is a SAP Parameter attribute which is used to control Size of the work process specific statistic 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 .
Size of the statistic buffer. This buffer is locally allocated
for each SAP work process. It contains the collected Statistic
data before it is writen into the statistic file.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.