[OpenLayers-Users] Overlay Issue

[Christopher Schmidt]

On Thu, Sep 13, 2007 at 05:14:19PM -0700, Paul Ramsey wrote:
> Anyone seen this before? Pretty simple page (add map, add two layers, 
> one yahoo, one wms overlay):
> 
> http://mapserver.refractions.net/openlayers/index.html
> 
> Try some longish pan'drags. I am getting the WMS layer frozen quickly. A 
> zoom out and back in fixes it up again.
> 
> Same thing happens w/ VE underlay.

I think that this is the result of a badly behaving server. I watch
tcpdump output, and I see a ton of:

  1.209096 192.168.1.51 -> 142.32.8.196 TCP 50287 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.214622 192.168.1.51 -> 142.32.8.196 TCP 50288 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.220198 192.168.1.51 -> 142.32.8.196 TCP 50289 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.225785 192.168.1.51 -> 142.32.8.196 TCP 50290 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.231705 192.168.1.51 -> 142.32.8.196 TCP 50291 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.237845 192.168.1.51 -> 142.32.8.196 TCP 50292 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.243856 192.168.1.51 -> 142.32.8.196 TCP 50293 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0
  1.249747 192.168.1.51 -> 142.32.8.196 TCP 50294 > http [SYN] Seq=0
Ack=0 Win=65535 Len=0 MSS=1460 WS=0 TSV=1125555350 TSER=0

with no traffic moving back and forth. 

Have you run into this situation with other WMS servers? It definitely
feels specific to this one: i've tried other WMSes over the Yahoo and VE
layers while debugging this and had no bad behavior.

The level of locking up that FF is doing for me is impressive enough
that I don't think that OL is likely the most responsible here. though
it's possible/likely that the server is getting hosed by many tiled
requests and choking and failing at the HTTP or lower level.

Trying an untiled layer might help:
http://openlayers.org/~crschmidt/pramsey-ve.html works for me,
sometimes, but I am definitely seeing a lot of misbehavior on the WMS
side as far as speed goes, so it wouldn't surprise me if it just feels
'hammered' by a tiled OpenLayers map.

Regards,
-- 
Christopher Schmidt
MetaCarta