Re: Bug in huge simplehash

Andres Freund писал 2021-08-13 12:21:
> Hi,
> 
> On 2021-08-10 11:52:59 +0300, Yura Sokolov wrote:
>> - sizemask is set only in SH_COMPUTE_PARAMETERS . And it is set in 
>> this way:
>> 
>>         /* now set size */
>>         tb->size = size;
>> 
>>         if (tb->size == SH_MAX_SIZE)
>>                 tb->sizemask = 0;
>>         else
>>                 tb->sizemask = tb->size - 1;
>> 
>>   that means, when we are resizing to SH_MAX_SIZE, sizemask becomes 
>> zero.
> 
> I think that was intended to be ~0.

I believe so.

>> Ahh... ok, patch is updated to fix this as well.
> 
> Any chance you'd write a test for simplehash with such huge amount of
> values? It'd require a small bit of trickery to be practical. On 
> systems
> with MAP_NORESERVE it should be feasible.

Which way C structures should be tested in postgres?
dynahash/simplhash - do they have any tests currently?
I'll do if hint is given.

>>  static inline void
>> -SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint32 newsize)
>> +SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint64 newsize)
>>  {
>>      uint64        size;
>> 
>> @@ -322,11 +322,7 @@ SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint32 
>> newsize)
>> 
>>      /* now set size */
>>      tb->size = size;
>> -
>> -    if (tb->size == SH_MAX_SIZE)
>> -        tb->sizemask = 0;
>> -    else
>> -        tb->sizemask = tb->size - 1;
>> +    tb->sizemask = (uint32)(size - 1);
> 
> ISTM using ~0 would be nicer here?

I don't think so.
To be rigid it should be `~(uint32)0`.
But I believe it doesn't differ from `tb->sizemask = (uint32)(size - 1)`
that is landed with patch, therefore why `if` is needed?

> 
> Greetings,
> 
> Andres Freund