Re: pgsql: Generational memory allocator

Hi,

On 2017-11-25 14:50:41 -0500, Tom Lane wrote:
> I wrote:
> > Tomas Vondra <tv(at)fuzzy(dot)cz> writes:
> >> BTW I also see these failures in hstore:
>
> >> ==15168== Source and destination overlap in memcpy(0x5d0fed0, 0x5d0fed0, 40)
> >> ==15168== at 0x4C2E00C: memcpy@@GLIBC_2.14 (vg_replace_strmem.c:1018)
> >> ==15168== by 0x15419A06: hstoreUniquePairs (hstore_io.c:343)
> >> ==15168== by 0x15419EE4: hstore_in (hstore_io.c:416)
>
> > Huh ...
>
> I tried to duplicate this on my RHEL6 workstation, and failed to,
> even though adding an assertion easily proves that the hstore
> regression test does exercise the case. So apparently the answer
> as to why skink isn't reporting this is just "not all versions of
> valgrind check it".

I suspect that the issue rather is that the compiler will sometimes
replace the memcpy() with an in-line member-by-member version. That'll
not be visible as a memcpy to valgrind.

> Meanwhile, skink has come back with a success as of 0f2458f, rendering
> the other mystery even deeper --- although at least this confirms the
> idea that the crashes we are seeing predate the generation.c patch.

Hm, wonder whether that could be optimization dependent too.

Greetings,

Andres Freund