New overlay: Resiliency Map

After listening to Stfano Maffulli’s great talk on OpenStreetMaps for emergency prep: The view from San Francisco I added a resiliency overlay style based on his QGis based prototype (page #14 in the slides).

The style can now be selected in the “Overlays” form step.

It is still “Work in Progress” though, with Source available on GitHub

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Yesterdays outage

Yesterday afternoon the rendering daemon failed in an interesting way, the preview images were rendered for most map requests, but not the actual map files.

It turns out that the root cause was a rendering request for a rather large area that consumed all available memory, leading to a short phase of swapping, and eventually a hard out-of-memory kill. Somehow the rendering service didn’t recover from this properly, and so the following requests were not properly processed either.

I thought I had memory issues covered in the renderers systemd service, by setting LimitRSS, the apparent systemd equivalent for “ulimit -m”.

But it turns out I had been “StackOverflowed” on this. Looking at the systemd.exec man page I learned that:

“LimitRSS= is not implemented on Linux, and setting it has no effect.”

Now I have replaced LimitRSS in the renderers service file with MemoryMax, and this actually seems to do the job. I re-ran all failed requests. This time the “bad” request still failed as it consumed too much memory, but it failed when reaching the set limit of 50% of total RAM already, without driving the system into swapping, and the following requests were properly processed again.

Hopefully this now has fixed “runaway memory” issues once and for all, not by preventing them in the first place, but by properly handling them when they occure, letting just that one render request fail, but not the following ones in the queue.

QR-Code overlay

I actually added the ability to add a QR code on the map to the renderer backend quite a while ago, but up to now it was only accessible via a command line parameter when starting the renderer directly.

This has now changed, and the web interface now offers a new QR code effects overlay. For now the endoced text is fixed to the request URL of the rendered map itself, but as soon as I’ve finished my plans for allowing for input of extra overlay customization parameters the QR code content will be freely customizeable.

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Some basic PDF hyperlink support

I’ve started to add some hyperlinks to the multipage PDF output, now that CairoGraphics and PyCairo support this.

For now only the “next page” arrows on the edges of the detail map pages are linked to the target pages in the PDF:

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UPDATE: The page rectangles on the overview now link to the detail pages, too

Continue reading “Some basic PDF hyperlink support”