ENH: ArchiveTimePlot Fetch Data on X-Axis Change

[zdomke]

This change prompts the ArchiveTimePlot to get data from the Archiver Appliance every time the x-axis' range changes.

Previously, archive data was only fetched when the user showed a section of the plot that had no data. With this set up, zooming out will fetch a optimized data (averaged w/ min/max error bars), but zooming back in would still optimized data. This results in the "resolution" looking wrong.

Now zooming in on a section will get the data for the time range shown on the plot. This will result in showing the correct "resolution" at all times.

[zdomke]

As I'm reading back through my code, I'm wondering if this should be an optional change. Should add a parameter to the ArchiveTimePlot constructor for getting data like this.
Some users may prioritize plot speed over curve resolution, especially if their archiver appliance is slow.

[zdomke]

Made the changes optional so that it can be enabled/disabled as required.
Split PyDMArchiverTimePlot.updateXAxis into multiple functions as it was getting big and messy.
Removed the update_immediately parameter from PyDMArchiverTimePlot.updateXAxis as it seemed unused.

[YektaY]

This looks good to me. I appreciate you breaking up the content in updateXAxis into smaller methods, it makes it easier to read :)

[jbellister-slac]

Thank you very much for the clean up! And the functionality is working well.

I think my only main concern is that it's possible to set up a plot without caching in such a way that it would call archiver every second if the PV is updating at 1Hz. (A short timespan would cause the x axis to move on every update). Defaulting cache_data to true is a good idea, but maybe we can still guard against that possibility.

[zdomke]

... it would call archiver every second if the PV is updating at 1Hz. (A short timespan would cause the x axis to move on every update). Defaulting cache_data to true is a good idea, but maybe we can still guard against that possibility.

You're right, this can be an issue. I was told not to worry about it because our archiver appliance can handle it, but I shouldn't assume that's true of everyone's setup.

I'm trying to come up with some way of reducing those calls.

[nstelter-slac]

nice!