[OSM-dev] osm2pgsql tile expiry freaks me out

[Steve Hill]

On Wed, 4 Nov 2009, Frederik Ramm wrote:

> The
> corresponding osm2pgsql tile expiry list for zoom level 18 (done with -e
> 18-18) has 5.6 GB and claims to mark dirty a whopping 350 million
> objects.

Ouch.  That sounds very high.  However, I don't think I've ever tried 
running with "-e 18-18", I use "-e 0-17" on OpenPisteMap.

> As you can see, the average number of edits in a 15-minute window is
> around 50k, but the number of expired tiles varies wildly beyond belief.

I'm not sure you can draw any conclusions from the number of expiries 
varying wildly.  For example - an edit that changes a single node is only 
going to affect a few tiles, whereas an edit that changes a relation made 
up of many objects has the potential to affect very large numbers of 
tiles.

> I'm in the process of instrumenting osm2pgsql to find out what changes
> generate these huge tile lists but maybe someone has a hunch.

I'm afraid I can't think of anything off the top of my head, the expiry 
stuff was running on OpenPisteMap quite successfully over several months 
after I implemented it.  Unfortunately, I'm not currently doing updates to 
OpenPisteMap (pending some replacement hard disks and Postgres tuning) so 
I can't tell you if anything has broken recently.

I'd certainly be interested in anything you find out though.

-- 

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence