Re: Segmentation fault when max_parallel degree is very High

On Wed, May 4, 2016 at 11:01 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Dilip Kumar <dilipbalaut(at)gmail(dot)com> writes:
>> When parallel degree is set to very high say 70000, there is a segmentation
>> fault in parallel code,
>> and that is because type casting is missing in the code..
>
> I'd say the cause is not having a sane range limit on the GUC.
>
>> or corrupt some memory. Need to typecast
>> *i * PARALLEL_TUPLE_QUEUE_SIZE --> (Size)i * **PARALLEL_TUPLE_QUEUE_SIZE *and
>> this will fix
>
> That might "fix" it on 64-bit machines, but not 32-bit.

Yeah, I think what we should do here is use mul_size(), which will
error out instead of crashing.

Putting a range limit on the GUC is a good idea, too, but I like
having overflow checks built into these code paths as a backstop, in
case a value that we think is a safe upper limit turns out to be less
safe than we think ... especially on 32-bit platforms.

I'll go do that, and also limit the maximum parallel degree to 1024,
which ought to be enough for anyone (see what I did there?).

--
Robert Haas
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