Hi Robert,
Great improvement! Memory usage dropped almost 6 fold for our paged scenes,
from oscillating around 350MB to rock solid 60MB (WinXP).
Many thanks,
Maciej
2008/3/28, Robert Osfield <[EMAIL PROTECTED]>:
>
> Hi All,
>
> Testing that I've been carrying out on some new big terrain databases
> has shown some real weaknesses in the DatabasePager ability to load
> balance - with memory footprint growing significantly when the camera
> moves fast over wide areas of high res data. Memory usage was growing
> to over 4GB and blowing our test computers, hardly something that is
> desired for a database paging system that is supposed to maintain a
> modest memory footprint.
>
> After much investigation the cause of the rather unconstrained memory
> usage has been traced to the slow speed that the DatabasePager was
> expiring (removing) no longer visible subgraphs - subgraphs were
> correctly ear marked for removal but idsyncrosies in the threading and
> original DatabasePager::removeExpiredSubgraphs(..) method meant that
> it would take many frames to finally let go expired subgraphs. It in
> fact was taking long enough that new data was coming in at a far
> faster rate than it was been removed at hence the dramatic growth in
> memory footprint.
>
> The solution has been to rewrite
> theDatabasePager::removeExpiredSubgraphs(..) method that is
> responsible for expiring subgraph and setting them aside for deletion.
> I've now got this new implementation working and sees a memory
> footprint halved which not affecting the visual quality on screen.
> Performance is now much more stable and crashes due to excessive
> memory consumption are gone on my test machine. With this rewrite a
> couple member variables and their associated set/getters are no longer
> required, and rather leave them around for potential confusion I've
> removed them completely so an svn update if you get an compile error
> just remove the below methods and recompile.
>
> - /** Set the maximum number of PagedLOD child to remove per frame
> */
> - void setMaximumNumOfRemovedChildPagedLODs(unsigned int
> number) { _maximumNumOfRemovedChildPagedLODs = number; }
> -
> - /** Get the maximum number of PagedLOD child to remove per frame
> */
> - unsigned int getMaximumNumOfRemovedChildPagedLODs() const {
> return _maximumNumOfRemovedChildPagedLODs; }
> -
> - /** Set the minimum number of inactive PagedLOD child to keep */
> - void setMinimumNumOfInactivePagedLODs(unsigned int number) {
> _minimumNumOfInactivePagedLODs = number; }
> -
> - /** Get the minimum number of inactive PagedLOD child to keep */
> - unsigned int getMinimumNumOfInactivePagedLODs() const {
> return _minimumNumOfInactivePagedLODs; }
>
> I would like to improve this method further still as I've already come
> up with a better load balancing algorithm to implement in this method,
> however, it'll take a while longer to implement, so rather than wait
> for this polished implementation I'm checking in what is working
> effectively, albeit not perfect it is far better than what was there
> before.
>
> There are other aspects of the DatabasePager that need attention too,
> such as the high cost of DatabasePager::requestNodeFile() method
> during cull traversal when many file requested are queued up. This is
> something that has been raised on the list before by others, so it's a
> bit of common theme when we really start to push the size of paged
> databases we are dealing with. I will be spending more time on this
> code over the coming month, so feel free to chip in with your own
> experiences.
>
> Cheers,
> Robert.
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> osg-users@lists.openscenegraph.org
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>
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