Re: Vacuum: allow usage of more than 1GB of work mem

On Wed, Dec 28, 2016 at 3:41 PM, Claudio Freire <klaussfreire@gmail.com> wrote:
>> Anyway, I found the problem that had caused segfault.
>>
>> for (segindex = 0; segindex <= vacrelstats->dead_tuples.last_seg; tupindex =
>> 0, segindex++)
>> {
>>     DeadTuplesSegment *seg =
>> &(vacrelstats->dead_tuples.dead_tuples[segindex]);
>>     int            num_dead_tuples = seg->num_dead_tuples;
>>
>>     while (tupindex < num_dead_tuples)
>>     ...
>>
>> You rely on the value of tupindex here, while during the very first pass the
>> 'tupindex' variable
>> may contain any garbage. And it happend that on my system there was negative
>> value
>> as I found inspecting core dump:
>>
>> (gdb) info locals
>> num_dead_tuples = 5
>> tottuples = 0
>> tupindex = -1819017215
>>
>> Which leads to failure in the next line
>>     tblk = ItemPointerGetBlockNumber(&seg->dead_tuples[tupindex]);
>>
>> The solution is to move this assignment inside the cycle.
>
> Good catch. I read that line suspecting that very same thing but
> somehow I was blind to it.

Attached v4 patches with the requested fixes.