Re: BUG #13985: Segmentation fault on PREPARE TRANSACTION

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2016-02-25 09:51:49 -0500, Tom Lane wrote:
>> Marking pgprocno volatile is silly. What *is* missing is this:
>>
>> - ProcArrayStruct *arrayP = procArray;
>> + volatile ProcArrayStruct *arrayP = procArray;

> Well, that'll also force arrayP->numProcs to be loaded from memory every
> loop iteration. Not sure if we really want that.

I think we do. The entire point here is not to assume that that storage
isn't changing.

> What bothers me about this right now is that we currently write the
> pgprocno array with:
> memmove(&arrayP->pgprocnos[index + 1], &arrayP->pgprocnos[index],
> (arrayP->numProcs - index) * sizeof(int));
> arrayP->pgprocnos[index] = proc->pgprocno;
> arrayP->numProcs++;
> afaics there's absolutely no guarantee that memmov() will only use
> aligned sizeof(int) writes.

Ugh. That's a separate problem, but yes, it's a problem.

Seems like we can either (1) get rid of that memmove in favor of
a handwritten loop, or (2) give up on unlocked access to the
pgprocnos array. Which performance hit would you rather take?

regards, tom lane