On Sat, Feb 14, 2015 at 8:05 PM, Jody Garnett <jody.garn...@gmail.com>
wrote:
> If there is activity in this space I would be interest in setting up a
> multi threaded renderer and retiring the multithreaded renderer in uDig
> (but in the context of GeoServer):
>
I'm copying and pasting an answer I gave to someone that recently asked
about a multithreaded renderer uDig style,
that is, layer parallel:
No, there is no way to render in parallel multiple layers in the same
> request. The renderer actually has two threads, one that reads the data,
> simplifies it, locates the right style,
> and a second one that only does the painting of simplified geometries plus
> styles.
> That said, the problem has been analyzed in the past, and the bottleneck
> is not in reading the data, but in rendering it, the Oracle JDK basically
> does not allow two shapes to be painted concurrently at the whole JVM
> level.
> So the first thing I suggest is to either use OpenJDK (available on Linux
> only) or to install the Marlin renderer in your JDK:
>
> http://www.geo-solutions.it/blog/developerss-corner-achieving-extreme-geoserver-scalability-with-the-new-marlin-vector-rasterizer/
>
As a historical notice, a full rendering parallelization has been attempted
> in uDig project some years ago (uDig uses the same underlying library as
> GeoServer, in particular, GeoTools, to read and render) with bad results,
> the tool was making the whole operating system unusable by trying to read
> too many files in parallel, and/or putting the database on its knees due
> too many concurrent queries running (think of it, what if each request uses
> 10 connections, and you have 50 concurrent connections). We solved that by
> limiting the amount of parallel execution so that each resource would not
> have too many threads hitting it.
> Moreover, to support that, one would have to allocate N drawing surfaces,
> one per layer, which means the memory requirements for a single WMS request
> would be multiplied by the number of layers in the request, which is again
> not scalable (a WMS client can put a list of layers as long as it desires
> in a WMS request, there are no formal limits besides the length of the URL
> itself).
(the "tool" was uDig btw)
Long story short, a layer parallel renderer seems suitable for desktop
usage (where you have one request at a time, and 8-16GB of memory to play
with),
but if you want to go server side, you either have relatively low load, or
a truckload of memory (and once you go there, you need to change JVM, and
probably use some non free one like Azul).
And I have to contrast this with people that keep on asking me if a 2/4GB
VMWare machine/Amazon cloud instance is enough to run GeoServer ;-)
And you first need to make parallel painting go fast, by adding Marlin into
the mix, but this is more a problem of being willing/authorized.
Do you have any more experience/observation on the subject?
Cheers
Andrea
--
==
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==
Ing. Andrea Aime
@geowolf
Technical Lead
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