[OpenLayers-Users] WMS requests executed twice

[Andreas Hocevar]

Hi,

for single tile layers, this should be easy to debug: on a map with
just one layer, set a breakpoint in the setImgSrc method of
OpenLayers.Tile.Image, and look at the call stack to see in which
context it was called.

Thanks for digging into this!
Andreas.

On Wed, Feb 8, 2012 at 5:14 PM, Jan Hartmann <j.l.h.hartmann at uva.nl> wrote:
> No, "OpenLayers.IMAGE_RELOAD_ATTEMPTS = 0" didn't make any difference ( it
> is the default, anyway). Even so, things are much better than with
> OpenLayers 2.11: I only see a double request for some maps at some scales,
> but I find it difficult to pinpoint what happens. If you have any
> suggestions how to debug this, I'll try to look at it in detail: it's
> important for me to get this proxy-setup right. It could be a proxy problem,
> although I doubt it.
>
> Jan
>
> On 02/08/2012 04:33 PM, Andreas Hocevar wrote:
>
> Hi,
>
> if what you suspect is true, then the only explanation I have is that
> you have OpenLayers.IMAGE_RELOAD_ATTEMPTS set to something else than
> 0. If you set it to 0, no request should be sent twice. So you could
> check that.
>
> Andreas.
>
> On Wed, Feb 8, 2012 at 3:29 PM, Jan Hartmann <j.l.h.hartmann at uva.nl> wrote:
>
> No, I was too fast: the problem still shows up sometimes, even with the
> development version of OpenLayers. It looks like OpenLayers does a second
> request when the webserver takes a long time to return a single-tiled map.
> For example, I see a single request when requesting a WMS service on the
> same server within a private network, and two requests when the request
> comes from the outside and has to pass several proxies to get to the
> webserver. Also, low-resolution images are served once, high-resolution ones
> sometimes twice. It is a bit unpredictable, but could that be he problem?
>
> Jan
>
> On 02/06/2012 06:19 PM, Andreas Hocevar wrote:
>
> Hi,
>
> this was a big change
> (https://github.com/openlayers/openlayers/commit/23c909220159134d270064bc4c89440c59c22d20)
> which fixed a lot of things. In your case in particular, we now don't
> create a new IMG element for the backbuffer, but keep the existing
> image, and instead we create a new IMG element for the next tile (i.e.
> the new extent for single tile layers). For tiles without a cache
> header (which might get stripped by a proxy), the old behavior meant
> that the tile is re-requested for the backbuffer.
>
> Andreas.
>
> On Mon, Feb 6, 2012 at 12:21 PM, Jan Hartmann <j.l.h.hartmann at uva.nl> wrote:
>
> Yes, it *was* that issue: with the development version of OpenLayers layers
> are always retrieved just once. Thanks Andreas. Just curiosity, can you give
> me a pointer to what the problem was?
>
> BTW, I don't get all messages from the OpenLayers Users list in my mailbox.
> Had to look up your answers in the archive.
>
> Jan
>
> ---------------------------------------------------------------------------------------
>
> Andreas Hocevar wrote on Mon, 6 Feb 2012 04:01:51 EST 2012
>
> Hi, just to clarify, the issue you are seeing (if it's the issue I think it
> is) was fixed *after* 2.11. Andreas.
> ----------------------------------------------------------------------------------------------
>
> Hi Andreas,
>
> No, I use OpenLayers 2.11. I see now that it has something to do with my
> proxy. All maps are on webservers in an internal network and are accessed
> via one proxy.When I run the page on the local server, maps are retrieved
> only once. When I access that same server from the outside, via the proxy,
> all maps are retrieved twice.
>
> Although this is probably not an OpenLayers problem, I would be gratefule
> for suggestions. It took me quite some time to get the proxy configuration
> running. It works now, but takes twice as much time as needed.
>
> Jan
>
> --------------------------------------------------------------------------------------------------------------
>
> Andreas Hocevar wrote on Mon, 23 Jan 2012 04:58:20 -0800: This might be due
> to a bug that has been fixed quite some time ago already. Which version of
> OpenLayers are you using? Andreas.
> On 01/21/2012 09:27 PM, Jan Hartmann wrote:
>
> Hi all,
>
> I made a very simple OpenLayers test site, displaying a simple local
> MapServer map as an untiled WMS service. Works fine, but when I look in the
> server log, each OpenLayer GetMap request results in *two* identical
> requests to the server. Can anyone confirm this, and why does it happen?
>
> Jan Hartmann
> Amsterdam
>
>
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-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.