Re: GC problem with lot of allocated memory

[Sean Conner <sean@...>]

It was thus said that the Great Hisham once stated:
> On 28 May 2016 at 19:24, Sean Conner <sean@conman.org> wrote:
> > It was thus said that the Great Rodrigo Azevedo once stated:
> >> The code
> >>
> >> N = 1.0e7
> >> C = {}
> >> for i=1,N do C[i] = i end
> >> print(collectgarbage("count"))
> >> for i=1,100*N do
> >>         local a = {1,2,3,4}
> >> end
> >> print(collectgarbage("count"))
> >>
> >> prints
> >>
> >> 262166.11035156
> >> 445760.78710938
> >>
> >> problem: when Lua uses lot of memory, the creation of temporary objects can
> >> consume all your memory. I think CG should collect the objects fast enough,
> >> but it does not. A perfectly OK program can't run because of the amount of
> >> garbage to be collected consumes all memory.
> >
> >   The code presented does not generate any garbage so there's not much to
> > collect.  To do some tests on my system, I had to change the code a bit:
> >
> > N = 25000
> > C = {}
> > for i=1,N do C[i] = i end
> > print(collectgarbage("count"))
> > for i=1,100*N do
> >         local a = {1,2,3,4}
> >         a = nil
> >         if i % 1000 == 0 then
> >            collectgarbage('count')
> >           --collectgarbage('step')
> >         end
> > end
> > print(collectgarbage("count"))
> 
> This got me intrigued: why is the `a = nil` necessary to make it
> "generate garbage"? I thought the `{1,2,3,4}` table would go out of
> scope even without it. Apart from the `if % 1000` block, shouldn't the
> two codes be equivalent?

  I misread the code and thought it was necessary.  It was some time after I
sent it that I realized my mistake.

  -spc