[OSM-talk] how long does it take from edit to slippy map?

[Frederik Ramm]

Hi,

 > I think there are some automated RSS feeds that flag up areas that
 > have been changed.

Yes, but not all changes are picked up by the feed used for tiles at home. 
If people upload many changes at once, or many people upload changes at 
once, then the feed may miss some of them. Another reason to "save 
early, save often" in JOSM.

 > I know that I & a whole bunch of people are running tiles at home scripts
 > that probably turn around a request for a re-render to uploading the
 > tiles in an hour or so.

The combined throughput of alle tiles at home participants is between 100 
and 400 tilesets per hour (a tileset being a level-12 tile and all 
level-13 to level-17 tiles contained therein). Of course rendering an 
individual tile will take longer than 1/100 of an hour but it seldom 
takes a full hour.

 > I guess that once those tiles are on the server they need to be
 > moved to where the slippy map can get at them.

The tiles at home upload receiver script unzips the tiles and stuffs them 
into the database immediately. *If* the database is available ;-), so 
there's not a big delay there.

tiles at home is quite efficient, but it is handicapped (at the moment) by 
a database overload ("too many mysql connections", broken images in the 
slippy map, sometimes willing renderers can't even be assigned a job 
from the queue because the database is unavailalbe). Also, once 
tiles at home has distributed your rendering request(s) to clients, it has 
no control about what they do. If one of the clients gobbles up the 
request but the upload is broken (or the machine went offline by the 
time there is data to upload), then your request may sit in the "being 
rendered" queue for quite some time, and you can't even re-request it.

If you want a particular tile re-rendered, it doesn't hurt to trigger 
rendering through the tile browser or informationfreeway.org, or even 
(if you're a Unix user) do what I do when I have made a lot of changes 
to the Karlsruhe map:

for x in 2142 2143 2144
do
     for y in 1405 1406 1407
     do
	wget -qO /dev/null "http://dev.openstreetmap.org/~ojw/NeedRender/?x=$x&
y=$y&priority=1&src=fred_rendering_karlsruhe"
     done
done

(modify according to your needs, and of course do that only if you have 
actually changed something, not from a cron job!)

 > So whats typical? If I get lucky could I see the changes in under an
 > hour?

You can watch it for yourself at 
http://dev.openstreetmap.org/~ojw/Log/Requests/ (database load 
permitting). If I request nine tiles like sketched above, and the queue 
is empty before (which it almost always is), the first results pop up 
after 15 to 20 minutes, but it can be several hours until the last tile 
is rendered.

 > What I've outlined I think is for the osmarender layer, what about the
 > mapnik layer - how long does that take from edit to shiney new tile?
 > Is that typically faster?

Mapnik is much faster than osmarender, but not used in a distributed 
environment which sort of nullifies that advantage. I believe there's a 
mechanism that will re-render tiles that have been looked at, but AFAIK 
it always uses the latest planet file, so if you change something on 
Wednesday afternoon, it will be at least 7 days until you see it up on 
the Mapnik layer. (Not a Mapnik expert though, may be wrong here.)

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'