Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I thought someone had tested that there was little/no performance
> difference between these two statements:
> MemSet(ptr, 0, 256)
> vs.
> i = 256;
> MemSet(ptr, 0, i)
But with any reasonably smart compiler, those *will* be the same because
the compiler can do constant-folding (ie, it knows i is 256 when control
reaches the MemSet). Pushing the MemSet into MemoryContextAlloc
eliminates the possibility of knowing the size argument's value.
> I can back out my changes, but it would be easier to see if there is a
> benefit before doing that. Personally, I am going to be surprised if a
> single conditional tests in MemSet (which is not in the assignment loop)
> will make any measurable difference.
Then why were we bothering? IIRC, this was being sold as a performance
improvement.
regards, tom lane
