[Tile-serving] openstreetmap-carto benchmark results

[Paul Norman]

> From: Andy Allan [mailto:gravitystorm at gmail.com]
> Sent: Friday, May 17, 2013 1:54 AM
> To: Paul Norman
> Cc: Frederik Ramm; tile-serving at openstreetmap.org
> Subject: Re: [Tile-serving] openstreetmap-carto benchmark results
> 
> a) What layers are *slower* than the XML version. I suspect the amenity-
> points and amenity-symbols ones are slower due to the attachments issue,
> but I want to avoid a few hours of refactoring if it only nets a 0.1%
> improvement. So identification of slower layers is very useful.

I won't be able to easily figure this out, since it would require manipulating osm.xml. I'm a bit reluctant to do this, because I really dislike mapnik XML.

> b) Which layers are just *slow* in both styles. Paul's graphs show a
> tremendous jump at zoom 13 which I find really interesting, since it's
> not obvious what features being drawn at that zoom level could account
> for such a large increase. 

If you look at time per square Mercator meter z13 and z14 are fairly similar, with z15 not being too far behind. I think the question is, why is z12 so fast, and are there optimizations we can move to z13?

> It might be a combination of things, but
> obviously if it's one layer in particular, that would be worth focussing
> on, rather than optimising layers at random.

Three slow layers are roads, buildings and admin. I'm sure there's more. Removing them speeds up z13 by 46%, 34% and 22% respectively. I doubt the buildings can be optimized - there's just a lot of objects, few of which can be omitted and few of which intersect the bbox and aren't within it.

> In the meantime, I continue to work on openstreetmap-carto with an eye
> to making it easier to work with as my first priority.

I've mainly worked on the .mml and SQL, and the parts I've worked on seem like a direct conversion from osm.xml and weren't particularly easy to edit.

I also want to re-format all the SQL - right now it's formatted to produce pretty mapnik XML with the \n and tabs, I'd much rather an easier to edit .mml.