expiremeta.pl causes duplicate touch operations of same metatile file

[stephankn]

I am currently checking whether to renew my 10 years old rendering stack. I had a closer look at expiremeta.pl and noticed that it touched files way more often than expected.

On my test setup I had in total 5 metatile files. Still the script issued 960 touch operations.
Unless this is fully covered by OS level filesystem cache, it can cause i/o problems. Calling the touch command unnecessary often also probably not the best in terms of performance.

Probably the script should collect metatile files to touch in a "unique" data structure and then touch only once.

To reproduce create a tile store with very few meta-tiles and feed in a larger expiry output from osm2pgsql. Attached are my input files and a console output where I print each touch command.
tirex-expiremeta-repro.zip