Monitor tserver page doesn't always load Dead Tablet Servers table

[jack-gitdev]

Describe the bug
The Dead Tablet Servers table on the Accumulo Monitor's tserver page does not consistently load, even though it has entries that can be displayed. Reloading using CTRL+F5 multiple times will eventually get it to load. Reloading can also cause the table to not load.

Versions (OS, Maven, Java, and others, as appropriate):

• Affected version(s) of this project: 2.1.4

To Reproduce
Steps to reproduce the behavior (or a link to an example repository that reproduces the problem):

1. Go to '{accumulo-monitor-url}/tservers'
2. Dead Tablet Servers table starts loading, then either loads fully or disappears.
3. Reload using CTRL+F5 to reattempt

Expected behavior
The Dead Tablet Servers table should load every time when there are entries to be displayed.

[dlmarion]

The code used to reload the dead tservers page is kicking off an async ajax call to reload the table data, then will show or hide the table based on whether or not the table is empty:

accumulo/server/monitor/src/main/resources/org/apache/accumulo/monitor/resources/js/tservers.js

Lines 75 to 84 in 0f6025e

	function refreshDeadTServersTable() {
	ajaxReloadTable(deadTServersTable);
	// Only show the table if there are non-empty rows
	if ($('#deadtservers tbody .dataTables_empty').length) {
	$('#deadtservers_wrapper').hide();
	} else {
	$('#deadtservers_wrapper').show();
	}
	}

However, looking at the tservers.js file as a whole, it does not appear to be using the data stored in the session storage. Instead it appears to be re-fetching from the Monitor server. This could take much longer and may cause the table to be hidden.

[DomGarguilo]

I agree with @dlmarion analysis here. The async call is kicked off then immediately the code checks the length of the current data which can definitely be the stale data since the async call probably hasnt completed yet. I think the best fix would be to move the logic that hides/shows the table into the DataTable setup. DatTables has a drawCallback option (docs here) that I think would be the best place to move that code to. That would fix the bug.

However, looking at the tservers.js file as a whole, it does not appear to be using the data stored in the session storage. Instead it appears to be re-fetching from the Monitor server. This could take much longer and may cause the table to be hidden.

I think this double fetching does exist and could be cleaned up but I am doubtful that it is causing any delays and I think its probably just the first async bug.

[ctubbsii]

Another quick fix is to never hide the table... just always show the table, even if it might be empty, because it's not causing any harm.

[ArbaazKhan1]

I can take a look at this