Gabriel Roldán created GEOS-5076:
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             Summary: Halo in SLD seems to cause GWC seeding to hang up
                 Key: GEOS-5076
                 URL: https://jira.codehaus.org/browse/GEOS-5076
             Project: GeoServer
          Issue Type: Bug
          Components: GWC
    Affects Versions: 2.1.3
            Reporter: Gabriel Roldán
            Assignee: Gabriel Roldán
             Fix For: 2.2-beta2


from email:
---
Hello GWC users,

I am using GeoServer with an embedded GeoWebCache (the issue is experienced in 
the 2.1 snapshot version shipped with the OpenGeo Suite 2.4.6 and 2.4.4 - 
haven't tested on 2.4.5) on Ubuntu 10.04 and have come across the following 
issue: the tiling of a large address point layer (4 million records) stops at a 
specific geographic position. The Tomcat process that runs Geoserver + 
Geowebcache just hangs at 100%, and the tiling process never finishes.
The only way to free up the CPU is to restart the Tomcat service.

The verbose log did not provide any error message:
http://dl.dropbox.com/u/16004984/GeoWebcache-spaceAround/verbose_log-tile_seeding.txt
However, it provided enough information to isolate the issue on a 41-features 
dataset, which is described below to help replication of the issue.


I have described a minimal test case (41 features, and a short SLD) that 
replicate the issue. The steps are:
1) load the data in a PostGIS database
The SQL file is available at:
http://dl.dropbox.com/u/16004984/GeoWebcache-spaceAround/20120424-test_tiling.sql

2) insert the corresponding record in geometry_columns table:
INSERT INTO geometry_columns (f_table_catalog, f_table_schema, f_table_name, 
f_geometry_column, coord_dimension, srid, type) VALUES ('', 'public', 
'test_tiling', 'the_geom', 2, 4283, 'POINT'); 

3) configure the layer in GeoServer
Native CRS: 4283 
Declared CRS: 4326 
Reproject native to declared 
Compute bounds from data 

4) SLD
Available at: 
http://dl.dropbox.com/u/16004984/GeoWebcache-spaceAround/classic_address.sld
Also, link the layer to this style in the layer definition.

5) Seeding
The issue can be experienced when generating the tiles for this layer at level 
19. The GeoWebCache tiling options used are: 
- 1 process 
- Re-seed 
- 900913 
- png
- start level: 19, end level 19 
- default (blank) bounding box 
The 32 tiles are not generated and the CPU goes up to 100% (it stays at 100% 
even after killing the task via the GeoServer/GeoWebCache web interface).


Our analysis / workaround
Removing the halo section from the SLD solves the issue. Setting the halo size 
to 0 pixels works as well. Configuring a 5px gutter from the web interface does 
not fix the issue (in 2.4.6 - haven't tried in 2.4.4).
My impression is that there is an issue with the SLD's text renderer on the 
border of a meta-tile (possibly a label crossing over meta-tiles), that even a 
1px halo can trigger.
Note: GeoTools seems to provision 1 px extra for the rendering area because of 
the font stroke width:
2012-04-25 13:20:03,216 DEBUG [geotools.rendering] - Expanding rendering area 
by 1 pixels to consider stroke width
... but it's not obvious from the log that anything is provisioned for the 
halo, nor the gutter.
Note: we're using the Tahoma font which is not on the Ubuntu system by default, 
we've installed it manually. Could this be an issue for the renderer or should 
it work for all fonts?


Any advice/feedback?
Thanks in advance!

Herve Senot
Groundtruth Mapping Systems, Australia

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