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