Specifies when to synchronize output, i.e. force that all channel data are
actually transmitted to the client:
`Connection means only at the end of the connection. This means that the
channels of all pending requests may be buffered - needs a huge amount of
memory
`Close means only when closing the output channel (after every response).
This means that the whole response may be buffered - needs a lot of memory.
`Flush means only when the flush method is called. This is a good idea
when one can control that.
`Write means every time the internal output buffer overflows. This is the
recommended setting in general.