[postgis-devel] Lame attempt at cascade union in sql

[Mateusz Loskot]

Martin Davis wrote:
> Java is much more efficient at memory allocation than C++ is (at
> least, using std C++ memory operations). So barring a stroke of
> genius in GEOS-land I think JTS is alway going to out-perform.

A bit OT, but I can and can not agree.
GC allocation implements more sophisticated allocation strategies and is 
typically faster than manually new'ed/malloc'ed storage in C/C++.

But allocating everything in dynamic storage on the heap, costs a lot.
In C++, programmer can and should follow the rule of "no allocation 
costs nothing" and prefer stack wherever possible.
In GEOS, I've found it as a major problem. GEOS mimics Java approach 
almost directly without incorporating C++ patterns and optimizations.

Next issue is that standard containers in C++ use standard allocators 
that solve most common cases and guarantee robustness on all platforms.
For special conditions, it's highly recommended to invent dedicated
allocators and use them with standard containers.
Custom allocators in C++ are likely out-perform Java allocators + its 
cost of garbage collector.

p.s. I hope I've hit principles of substantive discussion and you won't 
get my post as a holly war. Flame is not my intention.


Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org