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[Python-Dev] Have a big machine and spare time? Here's a possible Python bug.

Larry Hastings larry at hastings.org
Sun May 26 05:29:14 EDT 2019 
On 5/22/19 12:15 PM, Tim Peters wrote:
> There's a Stackoverflow report[1] I suspect is worth looking into, but
> it requires far more RAM (over 80GB) than I have). [...]
> But, for a start, it would be good to know if anyone else can actually
> reproduce the problem.
>
> [1] https://stackoverflow.com/questions/56228799/python-hangs-indefinitely-trying-to-delete-deeply-recursive-object


I have a computer with two Xeon CPUs and 256GB of RAM.  So, even though 
it's NUMA, I still have 128GB of memory per CPU.  It's running a "spin" 
of Ubuntu 18.10.

I compiled a fresh Python 3.7.3 --with-optimizations.  I copied the 
sample program straight off the StackOverflow page.  The program ran for 
about five and a half hours then exited normally.

During the run it printed:

    This gets printed!
    This doesn't get printed

Statistics reported by "time":

    19811.05s user 123.56s system 99% cpu 5:32:15.04 total

Checking in on it now and then, peak observed memory usage (as reported 
by "top") was just under 80GB.

I take it that the interesting part was confirming that "This doesn't 
get printed" gets printed when you have enough RAM for the program to 
run to completion.  So I guess there's no bug here? Just an observation 
about CPython's garbage collector being kinda slow?  Or maybe CPython gc 
+ swap = super bombad slow?


//arry/

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