[OSM-talk] using SRTM contours when editing

Dave Stubbs osm.list at randomjunk.co.uk
Mon Sep 15 12:35:30 BST 2008


On Mon, Sep 15, 2008 at 11:07 AM, Steve Hill <steve at nexusuk.org> wrote:
> On Sun, 14 Sep 2008, Andy Allan wrote:
>
>> And I might try full-world contours at some point to see how slow it
>> gets with several gigs in postgis!
>
> Time to buy a bigger hard drive? :)

330GB free... :-)


>
> Actually, I suspect PostGIS will probably cope quite well (speed wise)
> since it is a spacial database and should be able to cheaply select
> contours within the requested region.  Tiles which contain a lot of
> contours will be much slower to render than flatter areas though.
>

There's cheap and cheap though... we have 15GB RAM to play with and
I'm guessing that once the index gets too big to cache nicely the
performance will drop quite spectacularly (especially as the disc I/O
is not great). We use about 1-2GB for tile rendering, probably another
1GB for misc stuff, leaving about 12GB for the OS file caches that
postgres relies on, and that RAM has to manage the contours, the OSM
data, the meta files accesses to actually serve tiles, the coastline
shapes, and the hill shading tiffs.

It all hums along nicely at the moment, but might not with a 250GB
contours table... need to investigate this before jumping in


Dave




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