[mapserver-dev] MapCache seeding issues

Stephen Woodbridge woodbri at swoodbridge.com
Mon Jan 23 09:41:47 EST 2012

On 1/23/2012 9:01 AM, Smith, Michael ERDC-CRREL-NH wrote:
> All,
> I'm running a cache seeding and it will occasionally fail with
> unknown error (another thread/process failed to create the tile I was
> waiting for
> Unfortunately this stops the seeding and restarting takes about 30 mins
> while it reads through all the created tiles (I'm using a TIFF Cache) to
> see where to start (this is a cache for a MapServer WMS Tileindex of
> about 800,000 1m jp2 images).
> Is there any way to make the seeding continue even if it encounters an
> error (perhaps writing the errors to a log) or to restart the seeding
> quicker by passing the last seed location (something like 54820 157495 18)?


I wrote a seeder for another tile cache system in the past and the 
restart issue was an issue for me also. What I did was to create some 
sentinel files that indicated if a row was completed and when a metatile 
was complete. Then the seeder could check and skip completed rows and 
also check for complete metatiles in the row when it restarted. Putting 
them is a separate directory makes it easy to remove them later.

Also in my seeder, I could restrict it to only seed some specified row 
range or a bounding box, so that I could run multiple instances of it on 
separate threads or separate computers and have them all write to the 
same SAN device or write to local disks and later copy the tiles to the 
final cache area.

These might be useful features to consider adding to mapcache.


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