Re: Improving scalability of Parallel Bitmap Heap/Index Scan

> +/* Needed for sort template to work with pointers to PagetableEntry */
> +typedef PagetableEntry *PagetableEntryPtr;
>
> This is a workaround; let's fix it properly, like this:
>
> ST_POINTER_TYPE *a = (ST_POINTER_TYPE *) data;
> ST_POINTER_TYPE *pa;
> ST_POINTER_TYPE *pb;
> ...
>
> I see that Thomas already encountered that problem in the 0001 patch
> of that series:
>
> https://www.postgresql.org/message-id/attachment/120554/0001-Add-bsearch-and-unique-templates-to-sort_template.h.patch

Makes sense. I should have done that right away. Done in patch v2-0001.

> +#define ST_COMPARE(a, b) pg_cmp_u32((*(a))->blockno, (*(b))->blockno)
> ...
> +#define ST_COMPARE(a, b, base) pg_cmp_u32(base[*(a)].blockno,
> base[*(b)].blockno)
>
> There's a comment in common/int.h that says:
>
> * NB: If the comparator function is inlined, some compilers may produce
> * worse code with these helper functions than with code with the
> * following form:
> *
> * if (a < b)
> * return -1;
> * if (a > b)
> * return 1;
> * return 0;
>
> ...and that's been true every time it's tried. It should be fine to
> instead make the current comparators static inline and make both match
> the above pattern. You might get a further speed-up.
Oh, right. The qsort partitioning code does:

return DO_COMPARE(a, b) < 0 ?
(DO_COMPARE(b, c) < 0 ? b : (DO_COMPARE(a, c) < 0 ? c : a))
: (DO_COMPARE(b, c) > 0 ? b : (DO_COMPARE(a, c) < 0 ? a : c));

With the if-cascade the compiler can better optimize the expression in
DO_COMPARE().

I revived the original comparators with some minor modifications.
Runtimes of just the sorting now are:

master: 189 ms
patched v1: 136 ms
patched v2: 106 ms

Nice additional speedup!

--
David Geier