[OpenLayers-Users] Performance Issue with multiple layers

Marc Desharnais marc.desharnais at ec.gc.ca
Mon Aug 6 11:44:44 EDT 2007

Hi all,

Thanks Gregor, Stephen and Eric for your answers. I will investigate 
further with your advices.

Many thanks! :)


Stephen Woodbridge wrote:
> Eric Lemoine wrote:
>> On 8/6/07, Marc Desharnais <marc.desharnais at ec.gc.ca> wrote:
>>> Hi all,
>>> I don't know if it's normal, but my page using 7 layers is really slow.
>>> I have to mention that the layers are not all activated. Only 2 of them
>>> are shown of on the map.
>>> Initial loading takes up to 30 seconds. Zooming to a particular area :
>>> 10 seconds.
>>> And the CPU consumption of my workstation jumps up to 80% when loading
>>> times. Is this normal?
>>> Logically the workstation should not work really hard since it is
>>> querying some PNGs... Am I wrong?
>>> No server is on my workstation. The server and all the data used in the
>>> layers is on LAN.
>>> 6 layers are colored points and one is a shapefile converted to 
>>> postgis.
>>> What is slowing down the process?
>> Hi Marc,
>> Seven layers is a lot of layers, and is probably what kills you here.
>> Can't you merge your layers to reduce the number of layers in
>> OpenLayers?
> Marc,
> Depending on the type of layer you are using, this might make 7 image 
> requests if you are not using tiles and if these are all going back to 
> the same server then they will pretty much get serialized unless you 
> play some DNS tricks to give the server multiple CNAMES.
> If you are using tiles, you might be loading 9-25 tiles for each layer 
> times 7 layers and the same issues I mentioned above would apply.
> This is why Mark has suggested combining layers into a single request 
> if your user model will allow for that.
> You can use Foxfire and FireBug to monitor the time to load the 
> various images and this will give you a better idea of where the time 
> is getting spent. You should also watch the server and see if it is 
> the bottle neck and how many requests is is getting and processing.
> Hope this explains your issue a little better.
> -Steve W

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