ArchiveTimePlot archiver data fetched only on redraw #1303
Description
I am trying to use the ArchiveTimePlot, which is a very nice feature, however fetching data from the archiver (when scrolling left or zooming out) in "cached" mode does not quite behave as expected (or maybe I'm just using it wrong).
It seems that there a request to the archiver is made only when updateXAxis() is called, which appears to happen in redrawPlot(), but only when self._needs_redraw is set.
When liveData=True, this seems to result in the request only being made once a new value for the PV is received. If the PV updates at a very low rate (say like every minute), this is a problem. Further, this also seems to imply that if liveData=False, data is never fetched from the archiver.
I assume using cache_data=False works around this, but presumably it would be a better solution if caching can be used.
I am testing this with this example, where I've replaced the PV with one that is available in my local network and archiver.