Map services taking a long time to load in Web Apps, but not in a fresh Web Map

[David_Brooks]

I'm troubleshooting my team's web apps. We're experiencing an issue where some layers are taking a long time to load, but when I open them in a fresh web map, they draw immediately. I've monitored the server CPU and RAM and all seem stable. Any ideas what's up there? Using WAB and Map Viewer Classic.

I'm also noticing that my services on shared instances are taking a long time to load on app/map start. But this is a separate issue not related to the slow map start in web apps.

Might consider switching most services to dedicate instances, but concerned this will use up all the available RAM and CPU.

[jcarlson]

WAB and Map Viewer Classic shouldn't behave any differently with respect to drawing features. We don't use WAB much over here anymore, but is it possible that the app is having trouble loading some widget or something that is coming earlier in the loading sequence?

I would try two lines of approach:

1. Create a brand new WAB app with no widgets in it, just the map. See if it still loads slowly.
   1. If yes, then the issue is something with WAB, though I'd be stumped as to exactly what.
   2. If it loads quickly in a no-widget app, try making a copy of one of your slow apps and remove widgets one at a time to see whether that makes a difference
2. When loading your WAB app, have your browser's network tab open and watch the traffic for any long-running queries or URLs returning errors.

We did experience something like this once, and it was the fault of a single reference layer we were pulling in from another source. But that impacted the Map Viewer the same as WAB, so it probably wasn't the same issue.

[David_Brooks]

@jcarlson  thanks for your advice. We were getting a lot of time-outs on the ArcGIS Server, and tracked it down to overloading shared instances. We increased the maximum heap size to 128MB, increased the number of shared instances from 4 to 8, and set some of the more resource intensive map services to dedicated, and this seems to have made everything much more stable. The next step is to increase our cores from 4 to 8 and double the ram 💪