Re: [HACKERS] Parallel tuplesort (for parallel B-Tree index creation)

On Mon, February 5, 2018 4:27 pm, Robert Haas wrote:
> On Mon, Feb 5, 2018 at 1:03 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>> It certainly is common. In the case of logtape.c, we almost always
>> write out some garbage bytes, even with serial sorts. The only
>> difference here is the *sense* in which they're garbage: they're
>> uninitialized bytes, which Valgrind cares about, rather than byte from
>> previous writes that are left behind in the buffer, which Valgrind
>> does not care about.
>
> /me face-palms.
>
> So, I guess another option might be to call VALGRIND_MAKE_MEM_DEFINED
> on the buffer. "We know what we're doing, trust us!"
>
> In some ways, that seems better than inserting a suppression, because
> it only affects the memory in the buffer.
>
> Anybody else want to express an opinion here?

Are the uninitialized bytes that are written out "whatever was in the
memory previously" or just some "0x00 bytes from the allocation but not
yet overwritten from the PG code"?

Because the first sounds like it could be a security problem - if random
junk bytes go out to the disk, and stay there, information could
inadvertedly leak to permanent storage.

Best regards,

Tels