[OSM-talk] Tile refresh on openstreetmap.org

Tom Hughes tom at compton.nu
Sun Mar 2 11:35:21 UTC 2014

On 02/03/14 11:20, Christoph Hormann wrote:
> On Sunday 02 March 2014, Tom Hughes wrote:
>>> Well - in principle i think re-rendering of very old tiles (like >2
>>> weeks age) at the low zooms should take precedence over style
>>> induced updates at the high zooms.  Not sure how feasible it is to
>>> implement this.
>> They do. The algorithm goes something like this:
>> * Update stylesheet, remembering time
>> * Render z0 to z10 in the background
>> * Mark planet as dirty, using saved time
>> * Start rendering z11 to z12 in the background
>> [...]
>> Note that nothing in z0 to z12 is marked dirty as a result of changes
>> to the data, so they only re-render when the style changes, or once a
>> month as a background job.
> That pretty much explains my observations.  By having one or several
> stylesheet updates within the monthly update cycle the actual update of
> some tiles is stretched from a month to the ~7 weeks i observed.

I have no idea how you reach that conclusion - literally everything up 
to z12 has been rerendered at least four times in the last month.

For tiles up to z12 a style change actually causes it to be rerendered 
more quickly than would otherwise happen.

Anything beyond z12 is entirely dependent on how busy the tile server 
you are using is and, other than the last two weeks when we have had 
four style updates, there should have been no problem with rerendering 
it if necessary.

 > The  solution i could envision would be to have a single render
 > queue for the pre-rendered tiles that is prioritized based on age
 > of the existing  tile, possibly modulated with the zoom level (i.e.
 > the age of the  lowest zooms could be considered more severe than
 > z11 and z12).

Given that all tiles up to z12 have basically the same age, because they 
are only rerendered as part of a batch update, it's not clear to me how 
exactly this is supposed to work.


Tom Hughes (tom at compton.nu)

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