[Tile-serving] Improving Render Times

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Hello all,

I set up a osm tile server a week ago but am not satisfied with the 
performance. The server has an 8 core processor, 16GB of RAM, and a 
single 1TB SSD. It took about 2 days to import the full planet.

Here are some benchmarks:

Total for all tiles rendered
Meta tiles rendered: Rendered 349391 tiles in 420199.62 seconds (0.83 
tiles/s)
Total tiles rendered: Rendered 22361024 tiles in 420199.62 seconds 
(53.22 tiles/s)
Total tiles handled: Rendered 349504 tiles in 420199.62 seconds (0.83 
tiles/s)
*****************************************************
Zoom 06: min:  0.3    avg: 47.4     max: 1932.3     over a total of   
2702.3s in 57 requests
Zoom 07: min:  0.3    avg: 13.7     max: 1806.6     over a total of   
3373.8s in 247 requests
Zoom 08: min:  0.4    avg:  4.2     max: 652.1     over a total of   
4293.0s in 1010 requests
Zoom 09: min:  0.4    avg:  1.7     max: 425.8     over a total of   
6737.1s in 4079 requests
Zoom 10: min:  0.4    avg:  4.2     max: 1353.2     over a total of  
69453.8s in 16368 requests
Zoom 11: min:  0.4    avg:  1.5     max: 636.8     over a total of 
100399.6s in 65506 requests
Zoom 12: min:  0.4    avg:  0.9     max: 214.0     over a total of 
233220.1s in 262124 requests
*****************************************************

As you can see, it's quite slow at times. Even generating the cache took 
much longer than I would like.

Is there anything I can do to get some more speed out of it? It seems to 
be SSD bottlenecked, not CPU bottlenecked.