Overlay display issue in VRS

[Nick Duriez]

Just recently, the OpenAIP map has started randomly missing parts of the display when the display is moved around or zoomed in/out.

Could there be anything causing this behaviour?

[openaip net]

Hi Nick,

this behavior is caused due to the frequent updates to the database. Airspace data updates usually and unfortunately happen in large batches where the complete data has to be removed first and then re-added. For each area an airspace occupies, tiles are scheduled to be deleted, then recalculated and added back into the tile cache. UK for example requires roughly 700K operations to update the complete area. This all takes place "behind the scenes" while meanwhile the fronted CDN will still deliver "old" tiles until they expire and the newly added tiles will be retrieved from the tile cache and added to the CDN cache. 

This process is fragile and not bullet proof yet - especially when it comes to large bulk updates that run alongside other requests from third-parties they may be "seeding" their own caches etc. Depending on how successful the re-generation process was and cache expiration time in the tile cache and/or the CDN, the map will end up with blank tiles that eventually fix themself later when being expired and re-fetched. Since most apps directly target our tile service, we have to run aggressive caching mechanisms to reduce the requests to the actual backend systems to reduce the already high costs for the service which will slow down this "self-healing" process. 

TL;DR : The above behavior is (just guessing as I cannot see the details of each tiles loaded) caused by the fact that the map client somehow requested tiles during an unfinished update process and got a blank/empty tile back. I will re-seed the cache for UK airspaces but it will take time to reflect in the apps, i.e. after the cache has expired and the new tiles are fetched from storage.

[Richard Gale]

Thanks for the TL;DR - makes sense. I've been having similar issues with UK Airspace as OP, even after clearing browser cache and local tile cache. I'll stop worrying that this is something at a local level at this point and wait for refreshed tiles to filter through.

Thank you for all your hard work on OpenAIP.

R.