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I'm having the craziest GeoServer experience right now and I was hoping to get some input on what might be causing this behaviour.

I'm using Apache Bench to benchmark rendering performance for a layer via GeoServer's WMS interface and accidentally discovered that the vector icon size has a very significant effect on performance. The image I'm rendering:

  • 25,000 point features
  • Single rendering rule in SLD
  • 1900x1200 pixels
  • Request concurrency is 5
  • GeoServer is 2.6.1
  • JVM is Oracle Java 7 SE
  • Not using native JAI

The SLD's single rendering rule looks like this:

<PointSymbolizer>
    <Graphic>
      <Mark>
        <WellKnownName>circle</WellKnownName>
        <Fill>
          <CssParameter name="fill">#FF0000</CssParameter>
          <CssParameter name="fill-opacity">1.0</CssParameter>
        </Fill>
      </Mark>
      <Size>
        <ogc:Literal>50</ogc:Literal>
      </Size>
    </Graphic>
</PointSymbolizer>

This chart shows how response time for the same request varies based on icon size

enter image description here

As this is a vector icon I had assumed that rendering any size had as much impact on performance as any other size, but it appears that beyond a certain size (perhaps 16px) performance begins to suffer and beyond 30px it drops dramatically.

This has obvious implications for how I author future SLDs but right now I am more interested in why this would happen. Any thoughts?

EDIT: With a little more investigation I have found that increasing the (scaled) size of a PNG icon gives a much more linear increase in rendering time and there is a size, for this particular layer, when PNG icons become faster than vector icons. I have also seen that the relationship between icon size and performance is more linear with a smaller number of features. As it looks like the number of features and icon size both interact to affect performance I can only assume this is related to memory usage, I'm just not sure exactly how.

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  • Which renderer are you using? – BradHards Dec 13 '14 at 2:57
  • Do I have a choice? I don't think I've come across this so far so if there is a default I'm probably using that one. – tomfumb Dec 13 '14 at 4:39
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    OK, just wondered if you were using the Marlin rasteriser. The default depends on your JVM. See geo-solutions.it/blog/… – BradHards Dec 13 '14 at 4:54
  • @BradHards thanks for the tip - I set up the Marlin renderer and it resulted in a significant performance gain in high-concurrency environments and also removed the spike in response time for larger vector icons (raster performance remains unchanged). – tomfumb Dec 15 '14 at 23:37
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You actually forgot to mention, nor included it in the graph, how you measure "icon size": 1) width/height on the X-axis, 2) pixel area of icon in number of pixels

I guess it is 1), based on regular icon sizes.

That probably explains your graph: the increase in icon area size as measured in number of pixels is quadratic, each doubling of the width, increases the area by a factor 4.

So the number of pixels that need to be processed / generated / rendered for your vector icons, increases considerably with the "size" / width of the icon, which seems roughly consistent with the results in your graph.

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    I'm not sure I agree - as I said in my edit raster icons don't show the same relationship, but also the vector rendering time plateaus around the high-30/low-40 pixels. The SLD snippet does show how I'm measuring size - with the content of the <Size> element – tomfumb Dec 15 '14 at 13:28
  • The vector images would need to be rasterized and with more pixels that becomes more work. – bugmenot123 Jan 10 '19 at 12:15

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