> On Dec 4, 2025, at 13:30, John Naylor <[email protected]> wrote:
>
> On Wed, Dec 3, 2025 at 3:22 PM Chao Li <[email protected]> wrote:
>> I played with this again today and found an optimization that seems to
>> dramatically improve the performance:
>>
>> ```
>> +static void
>> +radix_sort_tuple(SortTuple *begin, size_t n_elems, int level,
>> Tuplesortstate *state)
>> +{
>> + RadixPartitionInfo partitions[256] = {0};
>> + uint8_t remaining_partitions[256] = {0};
>> ```
>>
>> Here partitions and remaining_partitions are just temporary buffers,
>> allocating memory from stack and initialize them seems slow. By passing them
>> as function parameters are much faster. See attached diff for my change.
>
> The lesson here is: you can make it as fast as you like if you
> accidentally blow away the state that we needed for this to work
> correctly.
>
Yeah, I quickly realized I was wrong after I clicked “send". I was trying the
firs two optimizations as I suggested in my previous email, but the first
didn’t help much, and the second just didn’t work. After several hours
debugging, I guess my brain got stuck and came out the weird idea.
I continued playing with this again today. I think the execution time is mainly
spent on the in-place element switching, which uses 3 levels of loops
(while->for->for). If we can use an extra temp array to hold the sorted result,
then the 3-level loop can be optimized to 1-level, but that will cost a lot of
extra memory which I am afraid not affordable.
Anyway, it’s a fun of playing with this optimization thing. I may play with it
again once I get some time.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
