When does MT4 refresh HST file?

 
I want to read HST file with real time updates I wonder when does MT4 refresh these files? Can I keep them up to date in real time?
 
ama bamo: I want to read HST file with real time updates I wonder when does MT4 refresh these files? Can I keep them up to date in real time?

They are most likely cached/buffered in memory for speed efficiency, and only flushed to disk when predetermined conditions are met.

Why do you want to read the HST files directly anyway, when the data is fully accessible from within MQL4?