[boost] Is disabling boost log auto flush the only way to control the log flush? Or can you change log auto flush rate?

Hi, I use boost log in an embedded system where flushing log message to flash storage need be controlled. I could not find how to change log auto flush rate, is it the only way to disable auto flush boost::log::keywords::auto_flush = false? I think there must be a way to change a desired log flush rate value without disabling auto flush, appreciate any tips. Thank you. JHH