Re: asynchronous and vectorized execution

> -----Original Message-----
> From: pgsql-hackers-owner@postgresql.org
> [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of David Rowley
> Sent: Tuesday, May 10, 2016 2:01 PM
> To: Kaigai Kouhei(海外 浩平)
> Cc: Robert Haas; pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] asynchronous and vectorized execution
> 
> On 10 May 2016 at 13:38, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> > My concern about ExecProcNode is, it is constructed with a large switch
> > ... case statement. It involves tons of comparison operation at run-time.
> > If we replace this switch ... case by function pointer, probably, it make
> > performance improvement. Especially, OLAP workloads that process large
> > amount of rows.
> 
> I imagined that any decent compiler would have built the code to use
> jump tables for this. I have to say that I've never checked to make
> sure though.
>
Ah, indeed, you are right. Please forget above part.

In GCC 4.8.5, the case label between T_ResultState and T_LimitState were
handled using jump table.

TupleTableSlot *
ExecProcNode(PlanState *node)
{       :     <snip>       :   switch (nodeTag(node)) 5ad361:   8b 03                   mov    (%rbx),%eax 5ad363:   2d
c900 00 00          sub    $0xc9,%eax 5ad368:   83 f8 24                cmp    $0x24,%eax 5ad36b:   0f 87 4f 02 00 00
   ja     5ad5c0 <ExecProcNode+0x290> 5ad371:   ff 24 c5 68 48 8b 00    jmpq   *0x8b4868(,%rax,8) 5ad378:   0f 1f 84 00
0000 00    nopl   0x0(%rax,%rax,1) 5ad37f:   00
 

Thanks,
--
NEC Business Creation Division / PG-Strom Project
KaiGai Kohei <kaigai@ak.jp.nec.com>