use Devel::Peek;

my $n = 1_000_000;

my @q;
for ( 1 .. $n ) {
   push @q, undef;
   shift @q;
}

Dump( @q );
[download]

SV = PVAV(0x5588bbfb50c0) at 0x5588bbfe31b8
  REFCNT = 1
  FLAGS = ()
  ARRAY = 0x5588bbfee1d0 (offset=4)
  ALLOC = 0x5588bbfee1b0
  FILL = -1
  MAX = -1
  FLAGS = (REAL)
[download]

offset + MAX + 1 gives the size of the array buffer, which is 4. The memory "leak" described by the linked post does not exist.

Doesn't change anything if you prevent it from becoming empty.