3.2.1.1 MaxBuffer

The MaxBuffer option is used to control the size of the file buffer when PSE reads or writes. Use this to prevent large requests from swamping PSE and the web server.

This applies only to PSE itself. If you read or write to files in your own code (a page template or a plugin) then you control the buffering there via normal python means (pydoc file.read for more info).