I am setting up a tile server using the latest mod_tile build, so Mapnik 3.0.12. I noticed after doing all optimizations that some tiles were still serving particularly slowly so I:

  • Turned all layers off in the XML so it is only rendering the map background
  • Changed the tile directory to a RAM-mounted filesystem
  • Ran perf for 60 seconds and dragged around a slippy map a whole load to render lots of background-only tiles (not science, I know)

The result is a lot of tile requests with TTFB latencies ranging from 2ms to 600ms and a perf log that looks like this:

perf log

A background tile looks like this, no interaction required:

ocean tile

The server has loads of head room (2x Intel Xeon 5500s and 32GB of RAM). Any ideas?

Edit: The tiles with long waits are the ones which cause a new metatile to be rendered. If I watch the requests come through on the server all meta tiles are taking about the same time to render:

renderd[3150]: DEBUG: DONE TILE default 19 2848-2855 424-431 in 0.551 seconds
renderd[3150]: DEBUG: DONE TILE default 19 2848-2855 416-423 in 0.523 seconds
renderd[3174]: DEBUG: DONE TILE default 19 2856-2863 416-423 in 0.557 seconds
renderd[3174]: DEBUG: DONE TILE default 19 2856-2863 416-423 in 0.550 seconds
renderd[3174]: DEBUG: DONE TILE default 19 2864-2871 416-423 in 0.551 seconds
renderd[3174]: DEBUG: DONE TILE default 19 2864-2871 416-423 in 0.561 seconds
renderd[3174]: DEBUG: DONE TILE default 19 2864-2871 416-423 in 0.561 seconds

Is this a regular time for a 2048 x 2048px metatile? If I replace the background image with a colour it drops to about 450ms.

asked 30 Jun '16, 19:46

PeterDevoy's gravatar image

PeterDevoy
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accept rate: 0%

edited 02 Jul '16, 16:26

Maybe more relevant to create an issue in mod_tile or mapnik github? Or the tile-serving@ mailing list.

(01 Jul '16, 21:33) yvecai

Devs are a bit slow responding to issues on the repos, I will try the mailing list, thanks.

(02 Jul '16, 12:42) PeterDevoy

btw: the screenshot above shows save_as_png8_hex with 41%.

Follow up post is here: https://lists.openstreetmap.org/pipermail/tile-serving/2016-July/003961.html

(02 Jul '16, 15:45) mmd

Thanks, well spotted, I have updated the title.

(02 Jul '16, 16:25) PeterDevoy
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question asked: 30 Jun '16, 19:46

question was seen: 2,449 times

last updated: 02 Jul '16, 16:26

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