Re: Atomics for heap_parallelscan_nextpage()

On Wed, Aug 16, 2017 at 9:55 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2017-08-16 11:16:58 -0400, Tom Lane wrote:
>> Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
>> > A couple of 32-bit x86 buildfarm members don't seem to be happy with
>> > this. I'll investigate, but if anyone has a clue, I'm all ears...
>>
>> dromedary's issue seems to be alignment:
>>
>> TRAP: UnalignedPointer("(((uintptr_t) ((uintptr_t)(ptr)) + ((8) - 1)) & ~((uintptr_t) ((8) - 1))) != (uintptr_t)(ptr)", File: "../../../../src/include/port/atomics.h", Line: 452)
>> 2017-08-16 11:11:38.558 EDT [75693:3] LOG: server process (PID 76277) was terminated by signal 6: Abort trap
>> 2017-08-16 11:11:38.558 EDT [75693:4] DETAIL: Failed process was running: select count(*) from a_star;
>>
>> Not sure if this is your bug or if it's exposing a pre-existing
>> deficiency in the atomics code, viz, failure to ensure that
>> pg_atomic_uint64 is actually a 64-bit-aligned type. Andres?
>
> I suspect it's the former. Suspect that the shared memory that holds
> the "parallel desc" isn't properly aligned:

Clang has an -fsanitize=alignment option that may be useful here.

--
Peter Geoghegan