[THREDDS #FOV-665359]: THREDDS5 aggregated dataset made up from <scan> and <aggregation> tags incredibly slow WMS visualisation on Web map app

Greetings!

Sorry for the delay in getting back to you on this! We believe we have a simple 
fix for the extremely slow WMS performance when requesting a different 
projection than the data is stored in. Can you check your JAVA_OPTS in your 
tomcat setenv.sh? If you have the "-ea" option set, can you test if it helps 
performance to remove it? That option is in our docs but it actually is a debug 
option to enable asserts. It looks to me that an assert in a library used by 
edal-java (which we use for WMS) is very computationally intensive so that may 
be the whole issue.

Best,
Tara



Posted on: 20230112.0749 MST
================================================================
Hello Unidata team,

We are running THREDDS 4 for production and recently evaluating THREDDS 5.

We're particularly interested in the <scan> and <aggregation> tags that create 
"virtual" aggregated datasets from multiple NetCDF files on S3. And we achieved 
something similar to this:

https://coverage.ceos.org/thredds/catalog/TDS_aws.html?dataset=MUR25-JPL-L4-GLOB-v4.2

Taking the above production dataset from CEOS as an example, we want to 
visualise the gridded data on a Web map app such as https://nationalmap.gov.au/ 
via WMS protocol.

It's doable but incredibly slow, regularly ending up not having any 
visualisations. Tile-generating requests can take up to 17 seconds.

CEOS said they pre-rendered the tiles to work around. And we want to know if 
there are ways to speed up the tile-generating requests directly from THREDDS 5 
configuration or something else that you would suggest besides pre-rendering 
the "virtual" aggregated dataset.

To reproduce the issue, here are the steps:

  1.  Visit https://nationalmap.gov.au/ and switch to a 2D map of your choice 
by clicking the "Map Settings" button top-right corner.
  2.  Copy this WMS link: 
https://coverage.ceos.org/thredds/wms/scan-aggregation/MUR25-JPL-L4-GLOB-v4.2.nc?service=WMS&version=1.3.0&request=GetCapabilities
  3.  Click the "Explore Map Data" button top-left corner.
  4.  Switch to the "My Data" tab, then click the "Add Web Data" button, and 
paste the link there.

Both NationalMap and Coverage services above are production grade.

Thanks for your time, we're looking forward to your reply. Have a good day!

Regards,












Ticket Details
===================
Ticket ID: FOV-665359
Department: Support THREDDS
Priority: Critical
Status: Open
===================
NOTE: All email exchanges with Unidata User Support are recorded in the Unidata 
inquiry tracking system and then made publicly available through the web.  If 
you do not want to have your interactions made available in this way, you must 
let us know in each email you send to us.