Re: pgsql-server/src/backend executor/nodeAgg.c ut ...

Neil Conway <neilc@samurai.com> writes:
> tgl@postgresql.org (Tom Lane) writes:
>> code for more speed by marking some routines 'inline'.  All together
>> these changes speed up simple sorts, like count(distinct int4column),
>> by about 25% on a P4 running RH Linux 7.2.

> I didn't know we were still doing optimizations / features for 7.3 :-)

Normally I wouldn't have, but it was a sufficiently big win for the
amount of effort put in that I figured I'd commit it now instead of
later...

> But very interesting results -- the 25% percent improvement is really
> surprising. Do you think there's more low-hanging fruit in this area?

Well, I'd known for awhile that FunctionCall2 was a bit of a bottleneck,
so that change was on my to-do list.  I was looking at count(distinct
foo) because someone had complained about it being slow, and I saw that
the overhead of calling the datatype-specific comparison function was
really a large fraction of the runtime in this case.  Getting further
won't be so easy.  What I'm seeing with those commits is that the
top hotspots for count(distinct int4column) are

  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 39.61     30.07    30.07 289140554     0.00     0.00  comparetup_datum
 16.36     42.49    12.42 16777216     0.00     0.00  tuplesort_heap_siftup
  5.22     46.45     3.96 289140558     0.00     0.00  btint4cmp
  4.37     49.77     3.32 25169576     0.00     0.00  AllocSetAlloc
  2.37     51.57     1.80 33554460     0.00     0.00  GetMemoryChunkSpace

(this is everything above 2% of the runtime).  comparetup_datum includes
inlined ApplySortFunction and FunctionCall2 overhead here, and I'm not
sure how we can get it down much further.

> Also, is the use of inline functions encouraged instead of macros?

I think it's okay for stuff that you are willing to tolerate possibly
not having inlined.  There is no portability issue because configure
takes care of providing a suitable "#define inline" if needed --- but
on some compilers it'll be #define'd as empty.

            regards, tom lane