Re: BUG #14722: Segfault in tuplesort_heap_siftup, 32 bit overflow

On 07/06/2017 01:14 AM, Andres Freund wrote:
> On 2017-07-05 18:03:56 -0400, Tom Lane wrote:
>> I don't like s/int/int64/g as a fix for this.  That loop is probably
>> a hot spot, and this fix is going to be expensive on any machine where
>> int64 isn't the native word width.  How about something like this instead:
>>
>> -		int			j = 2 * i + 1;
>> +		int			j;
>>
>> +		if (unlikely(i > INT_MAX / 2))
>> +			break;		/* if j would overflow, we're done */
>> +		j = 2 * i + 1;
>> 		if (j >= n)
>> 			break;
>
> Isn't an added conditional likely going to be more costly than the
> s/32/64/ bit calculations on the majority of machines pg runs on? I'm
> quite doubtful that it's worth catering for the few cases where that's
> really slow.

Another option to use "unsigned int", on the assumption that UINT_MAX >= 
INT_MAX * 2 + 1. And to eliminate that assumption, we can use (UINT_MAX 
- 1) / 2 as the maximum size of the memtuples array, rather than INT_MAX.

- Heikki