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[las_users] how to frequently update thredds dataset in las



Hi,

We're setting up a configuration where a Thredds dataset is accessible through LAS. The dataset is a regularly updated Thredds aggregation of ncml files, an oceanographic forecast generated with ROMS. The Thredds dataset has the same URL before and after the update.

At the moment we are using addXML to regenerate the relevant section of las.xml, then using tomcat manager to reload the las servlet to pick up these changes (in normal operation only the time arange element will change in the las dataset).

This method of regenerating the las dataset is not ideal for a couple of reasons:

1. Ideally we would use a natural dataset id rather than the one generated from addXML (the id is based on a hash of the thredds url, so it is persistent which is good, but it is not humanly interesting) 2. Ideally we would use natural variable names rather than those generated by addXML (perstent but not humanly interesting) 3. After a number of reloads of the las servlet, tomcat process runs short on PERM GEN space, which requires restarting the tomcat server to resolve.

I have looked into a couple of ways of improving the situation:

i. use script to generate the las dataset xml setting the arange to the new values, then reloading the LAS servlet. This would address most of the issues noted above, but not number 3.

ii. modify the las.xml dataset in such a way that it will still work after the thredds dataset has been updated. I've tried two options a. Remove the time arange from the las dataset. This breaks the las gui (date control vanishes) and also the wms service (including GetCapabilities). b. Set the time arange to an early start date with a large number of steps. This works in the las gui provided the user knows the correct date to pick, but still breaks wms.

My suspicion is that if I do not reload the LAS servlet we will also encounter problems with LAS caching older views.

I welcome suggestions on other options for updating the las dataset after the thredds dataset has been updated.

Thanks,
Robert.

--
Robert Fuller, Applepie Solutions,
5 Woodlands Avenue, Renmore, Galway, Ireland.
+353.86.0507760  http://www.aplpi.com
Registered in Ireland, no. 289353


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