Colin Marquardt schrieb:
2009/11/25 Peter Körner
<osm-lists(a)mazdermind.de>de>:
Atm. the load on cassini is around 20 and the
diff imports are fighting
to stay up. I think it's cmarq's hillshade-generator takes the most
resources on cassini. top reports ~57.1% IO waiting so I think there's a
lot of disk going on.
This must have gotten worse as generate_tiles goes to lower zoom
levels. I can kill it and maybe run with a single thread or even some
artificial slowdown tonight. Right now it's three threads, which
wasn't a problem so far.
I don't think that this is necessary atm. I just
wanted to talk about
this upcoming issue. Can you estimate how long it will keep running with
the current parameters? Getting some days out of sync is not that big
problem (we're not expiring tiles currently anyway).
I tried to do
a "du -hs /mnt/user-store/osm_hillshading" but ir ran
loooong until I canceled it.
Well, I generate hillshading for the land mass of Europe (plus the UK)
right now, so there isn't such a lot of empty sea tiles.
Okay, cool.
It would
indeed be nice to generate metatiles instead of the single PNGs
though.
Yes, it would. Is there a tool to pack the existing tiles into metatiles?
I'm also not rendering down to zoom 18.
Pre-rendering those
hillshading tiles (up to a certain zoom level at least) in general is
not bad IMO since they are very much static (they don't contain any
changing information), so will be useful for many maps for the next
several years.
Yes I see that, too, but rendering on the fly and then caching the
results is a compromise between disk space and cpu power.
Dynamically creating these tile (and then never
expiring them) would
also be possible if renderd or mapnik are extended, but right now,
only generate_tiles can do the necessary postprocessing.
Both problems
together create a real huge number of files in a single
directory which is not good for most filesystems. To make things worse,
/mnt/user-store is connected to cassini via NFS, so there's another
bottleneck.
We could determine what the maximum sensible number of files is in a
single directory and from that see up to which zoom level we could
support
It's not the absolute "max number" I'm worried about but
the decreasing
performance when working with a lot of files in a directory (and maybe
the inode usage). This could both be solved by using metatiles.
Peter