[Tilesathome] Questions on tile updating process

[Maarten Deen]

Andre Hinrichs wrote:
> On Samstag 18 April 2009, Maarten Deen wrote:
>> The only way I see for an external user is to load the details page for
>> every tile (http://tah.openstreetmap.org/Browse/details/tile/12/x/y/) and
>> get the "last modified" date.
>> But I don't think that would be very nice to the tah server.
> 
> Hmm.. since the tiles are processed sequentially I don't think, that would be 
> a real problem. To be honest, I've alread finished writing a small bash script 
> which is doing this. It's just finished processing Spain and Germany and it 
> seems to work fine.
> 
> Will not post it here, since it is partly a really dirty hack and it would not 
> be a good thing if too many people run this script in parallel.
> If someone is really interested, I will send it directly...
> 
> Here are the checks it does in order:
> 1.) Tile has an unhandled request -> ignore
> 2.) Tile has an active request -> ignore
> 3.) Tile is empty and was recently finished -> ignore
> 4.) Tile is empty and sea -> ignore
> 5.) Tile is empty and land -> rerender
> 6.) Tile is empty and mixed -> rerender
> 7.) Tile is empty and unknown -> ignore with warning
> 8.) Tile is no older than a given period -> ignore
> 9.) Tile is older than a given period -> rerender
> 10.) Tile is not empty and has no date -> ignore with warning

Ok, you're checking tiles as you go. My idea was to select the lowest renderdate 
and rerender that tile. That is less dirty but requires a database with the 
renderdates, or 16 million http requests to get all dates (which would make it 
an awful hack).

> Requests are being sent with priority 4 and source 'tile-reliability-checker'.
> Max age is currently set to one month since the tiles seem to have been 
> restored from a backup of 2009-03-04. At least I cannot see tile dates older 
> that date and younger than 2009-04-14.

There are. See tile (12, 2100, 1359) from 2009-01-14. There are more tiles in 
the Netherlands from januari.

> This situation results in rather high rate of render requests. I think in the 
> future the situation will get better.
> 
> The script takes approx. 0.4 seconds for each tile. Means, that for a complete 
> world check with 16 mio tiles it would take approx. 77 days to finish. Isn't 
> this a good result if the max age for a tile is set to two months???

Yup. Sounds as a reasonable hack for not having a direct access to all tile's 
renderdates.

>> That said: there are still wrong rules or renderers that use out-of-date
>> rules. I believe the issue of large names of waterfeatures and landfeatures
>> in lower zoomlevels has surfaced before, but it is still an issue. See tile
>> 12, 2111, 1353 at
>> <http://informationfreeway.org/?lat=51.957&lon=5.570&zoom=12&layers=B0000F0
>>00F> where the text "Neder Rijn" (and "Lingekanaal" in a neigbouring tile)
>> should not be there in zoom 12 and gets smaller in zoom 13 and 14 and gets
>> larger again from zoom 15.
>> I have requested rerenders of other tiles to see if it is a current
>> problem.
> 
> That looks to me like a very easy problem to fix... will look at it tomorrow... 
> err... today... after lunch...

I have requested some rerenders and that made the problem go away only half. See 
tile (12, 2106, 1359) which still has "Afwateringskanaal" in it. There was a 
second name which is now gone.

Regards,
Maarten