[OSM-talk] [OSM-dev] Software development - most pressing issues

[Tom Hughes]

In message <474EED36.3040207 at arjam.net>
          "Robert (Jamie) Munro" <rjmunro at arjam.net> wrote:

> Tom Hughes wrote:
>
> > You seem to have forgotten to rerender the tiles - just flushing as
> > bad as it means people will get the "here be dragons" tile until such
> > time as the tile is rerendered.
> > 
> > The current scheme largely never flushes - it just marks as dirty so
> > that they are (in due course) rerendered and until then it continues
> > to serve the old ones as that is better than a "coming soon" tile.
> 
> Mark them dirty rather than flushing is an improvement, yes. But
> currently, AFAIK, it marks all tiles as dirty once a week (or something
> like that) weather they have changed or not. If it didn't do this, the
> backlog could be reduced.

Incorrect. A tile which has been looked at, and is more than three
days old, is marked for rerendering. Tiles which are not looked at
are ignored.

With mod_tile we improve on that by knowing when planet was last
loaded which means (a) things don't have to wait three days if they
are rerendered just before the new planet is loaded and (b) we
don't rerender things when planet hasn't changed. It sill only
renders things which are looked at.

> What happened to the live on-demand rendering of tiles? I think it
> should try to render tiles that people are wanting to see now ahead of
> tiles in the backlog. It should only look at the backlog if it is not
> busy rendering current requests.

I think live rendering is pretty much permanently off now because the
queue is so long it wouldn't kick in anyway - it was only ever used
when the queue was short.

> Random other thought: Have we tried removing the highest 2 levels of
> zoom from the backlog? I.e. only ever show them rendered live? They
> would take up something 3/4 of the storage, but each tile individually
> is very unlikely to ever be looked at. They are also the fastest to
> rerender.

There is a separate script to render the top few zoom levels and that
does get turned off when the machine is busy I believe.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/