[mapguide-internals] Server rendering incomplete tiles - Defect or Feature??

[Martin Morrison]

"rasters are normally in a separate tile to other data right?" <- not necessarily...when you do tiling, you limit yourself to a fixed set of viewscales, that is not desired behavior for every site.

________________________________________
From: mapguide-internals-bounces at lists.osgeo.org [mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Zac Spitzer [zac.spitzer at gmail.com]
Sent: Tuesday, May 05, 2009 9:06 AM
To: MapGuide Internals Mail List
Subject: Re: [mapguide-internals] Server rendering incomplete tiles - Defect    or Feature??

rasters are normally in a separate tile to other data right?

so if the error normally produced a transparent tile then it would be ok right?
with a debug option to produce the error written on the tile (which
would be not cached)?

z

On Tue, May 5, 2009 at 9:19 PM, Martin Morrison
<martin.morrison at edsi.com> wrote:
> As long as it's an option...
>
> When I have a production box running well and some data (raster) stored on a second server, I don't want the whole site down because I had to reboot the second server.
>
> Martin
>
> ________________________________________
> From: mapguide-internals-bounces at lists.osgeo.org [mapguide-internals-bounces at lists.osgeo.org] On Behalf Of UV [uvwild at gmail.com]
> Sent: Monday, May 04, 2009 10:50 PM
> To: MapGuide Internals Mail List
> Subject: Re: [mapguide-internals] Server rendering incomplete tiles - Defect    or      Feature??
>
> So should I create an RFC to include an option to disable that behaviour
> in the config file and post a patch?
>
> Traian Stanev wrote:
>> It's classic MapGuide behavior to not take down the whole map because of a single layer -- a single layer that could be having intermittent issues with things like network connectivity to its data source for example. This is because most MapGuide applications have historically been live apps (and not offline tile generators).
>>
>> Traian
>>
>>
>> -----Original Message-----
>> From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of UV
>> Sent: Sunday, May 03, 2009 10:31 PM
>> To: MapGuide Internals Mail List
>> Subject: [mapguide-internals] Server rendering incomplete tiles - Defect or Feature??
>>
>> I studied the Stylize Layer code in MappingUtil.cpp.
>>
>> The exception handler (line 760-790) at the end of the layer loop is
>> catching exceptions and not doing anything about it (except logging)
>> AFAIK this would explain why the server generates incomplete == wrong
>> tiles without letting us know about it.
>> If I is misinterpeted the code please tell me why.
>>
>> WHATS HAPPENING
>>
>> Currently, mapping errors including the FDO access are replaced with a
>> simple log message
>> and the layer is omitted from the currently rendered tile. This gives
>> all kinds of visual effects on the tile.
>> On a large map its virtually impossible to identify the wrong tiles.
>> Just rerendering might require more than a day.
>>
>> Currently I believe the server is giving a wrong system response by
>> delivering such a faulty tile without note via the API.
>> This would be a major defect for this special class of use cases.
>> Furthermore, the relation between the log message and the offending tile
>> is very difficult to establish.
>>
>> If somebody thinks this is correct, please let me know why.
>>
>> POSSIBLE RESOLUTION
>> Rethrowing the exception will cause the server to return an exception
>> via the HTTP API causing the tile to fail also on the client side.
>> It will also stall the server eventually, very similar to the current
>> situation in that the workerthread will cease to serve requests.
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>
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--
Zac Spitzer -
http://zacster.blogspot.com
+61 405 847 168
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