I'm seeing a serious problem with my geoserver install, where it is crashing
the system it is running on, following certain types of WMS requests.
Given the fact that I am probably the only person on the list running
GeoServer (v2.0.0) under WebSphere App Server, using IBM Java, on AIX, I am
not expecting anybody to point me in the direction of a silver bullet.
However, if someone could confirm my theory as to what is happening that is
causing the issue in the first place, it might help. I'll try and talk
through an example, and my hypothesis - made with no knowledge of the
geoserver code whatsoever, I hasten to add! :)
FOR AN EXAMPLE WAYWARD REQUEST
I am rendering some vector data stored in Oracle Spatial. This data is
quite detailed, and from the geoserver debug logs, I can identify the exact
SQL used. I can run the SQL in sqlplus and the records return pretty much
instantaneously. There are eight polygons, and eight lines. The lines and
polygons have between 50 and 300 vertices, and are styled in different ways.
The MBR for these records is approx 2km by 1.5km.
These records render beautifully, and quickly (1-2 seconds) at 1:2000. [To
my simple mind, this suggests that the geometries are valid, and that the
styling is OK. I remember seeing an issue with symbols at these kind of
scales causing problems, but none of these records would be styled using
symbols. Basic lines and fills only]
As I zoom in (and in, and in) the rendering starts to take more time each
time, until I'm at something like 1:50. Rendering is now taking 20 seconds.
If I zoom in until I'm at 1:2 or 1:1, I can see the memory on the machine
be eaten up, until WebSphere starts paging like crazy and eventually the
machine hangs.
My theory is that GeoServer is trying to create an image at the same scale
as the target bbox, but containing the entire geometries pulled back from
Oracle. So if I request a 600x600 pixel image at 1:1 scale, it tries to
build an internal image that would contain the 2km x 1.5km - i.e., a (600 x
2000=1200000) x (600 x 1500=900000) image, before it would cut out the
600x600 bbox of interest.
Is this how it works?
GeoServer does have some WMS resource consumption limits that I can
configure, and I have these currently set to
Max rendering memory - 73728 KB (up from 64Mb, as I was seeing some
OutOfMemory issues on something else)
Max rendering time - 20s (down from 60s - see below)
Max rendering errors - 100 (down from 1000)
Changing the max rendering time seems to have helped, as GeoServer cant eat
all the available memory and pagespace inside 20 seconds (so far anyway -
touch wood!), but I would have hoped that if it was a memory issue, that the
limit stated here would be adhered to. I'd rather GeoServer barfed an
OutOfMemory error than it taking down my entire server. Should this limit
have stopped the problem?
The next thing for me to try (within GeoServer at least) is to try and set
up some MinScaleDenominators in the SLDs so that these features aren't
displayed beyond 1:10.
Are there any other suggestions on how to make this work/fallover
gracefully?
Any wise words gratefully received, as always.
Rob
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