Re: scalability bottlenecks with (many) partitions (and more)

On 9/22/24 17:45, Tom Lane wrote:
> Tomas Vondra <tomas(at)vondra(dot)me> writes:
>> I've finally pushed this, after many rounds of careful testing to ensure
>> no regressions, and polishing.
>
> Coverity is not terribly happy with this. "Assert(fpPtr = fpEndPtr);"
> is very clearly not doing what you presumably intended. The others
> look like overaggressive assertion checking. If you don't want those
> macros to assume that the argument is unsigned, you could force the
> issue, say with
>
> #define FAST_PATH_GROUP(index) \
> - (AssertMacro(((index) >= 0) && ((index) < FP_LOCK_SLOTS_PER_BACKEND)), \
> + (AssertMacro((uint32) (index) < FP_LOCK_SLOTS_PER_BACKEND), \
> ((index) / FP_LOCK_SLOTS_PER_GROUP))
>

Ah, you're right. I'll fix those asserts tomorrow.

The first is clearly wrong, of course.

For the (x >= 0) asserts, doing it this way relies on negative values
wrapping to large positive ones, correct? AFAIK it's guaranteed to be a
very large value, so it can't accidentally be less than the slot count.

regards

--
Tomas Vondra