[Geoserver-users] WMS GetCapabilities and time enabled layers

Richard Duivenvoorde

2017-07-12 14:20:09 UTC

Post by Jonathan Meyer
Our team deploys GeoServers fronting datasets regularly upwards of a
hundred million (occasionally billions) records. All our datasets are
time enabled which often causes issues for the responsiveness of our WMS
GetCapabilities. Everything goes fairly well as long as the aggregates
performed can take advantage of temporal indices (we use Postgres
primarily), but often new developers will create data missing indices or
with poorly performing joins. This affects all layer consumption, as we
heavily rely on GetCapabilities to self discover the available datasets
in our applications.
I saw a mailing list post from quite awhile back that also brought this
issue
up: http://osgeo-org.1560.x6.nabble.com/WMS-request-getcapabilities-takes-a-loooooooooooooong-time-to-return-td5003095.html
Has there been any thought for a GeoServer native solution for this?
Something as simple as a global setting that would allow caching
GetCapabilities with a configurable TTL would be tremendously helpful.
How are others solving this problem? Fronting GeoServer with a web cache
(Varnish or the like) to cache GetCapabilities requests that way? Never
enabling time dimension on layers when this is a problem?

One Apache trick I once saw in a situation like this is to make use of
the the fact that you can set up a 'ErrorDocument' in case of a file not
found/404 [0]. Apache can handle this (that is when files are not
available), and can then redirect to an alternative url (being the
actual geoserver url)

So one scenario you could try to set up:
- create an alias/url for a file (a static capabilities.xml doc) on the
filesystem which is served IF available
- if not available let Apache forward to the actual geoserver
capabilities xml to let geoserver create a fresh one for you
- depending on the trust you have in your dev's you can either let a
cronjob remove the file for you every x hours (which will be a problem
if one of the newby's did not set the right indexes anyway...)
OR you create a cronjob who requests the capabilities, and only on a
valid 200 then updates/replaces the capabilities.xml file.

Regards,

Richard Duivenvoorde

[0] https://httpd.apache.org/docs/2.4/custom-error.html

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