Re: Time to drop old-style (V0) functions?

2016-12-20 10:28 GMT+01:00 Andres Freund <andres(at)anarazel(dot)de>:

> On 2016-12-20 01:14:10 -0800, Andres Freund wrote:
> > On 2016-12-20 09:59:43 +0100, Pavel Stehule wrote:
> > > In this case some benchmark can be very important (and interesting). I
> am
> > > not sure if faster function execution has significant benefit on
> Vulcano
> > > like executor.
> >
> > It's fairly to see function calls as significant overhead. In fact, I
> > moved things *away* from a pure Vulcano style executor, and the benefits
> > weren't huge, primarily due to expression evaluation overhead (of which
> > function call overhead is one part). After JITing of expressions, it
> > becomes even more noticeable, because the overhead of the expression
> > evaluation is reduced.
>

For me a Vulcano style is row by row processing. Using JIT or not using has
not significant impact.

Interesting change can be block level processing.

>
> As an example, here's a JITed TPCH Q1 profile:
> + 15.48% postgres postgres [.]
> slot_deform_tuple
> + 8.42% postgres perf-27760.map [.] evalexpr90
> + 5.98% postgres postgres [.] float8_accum
> + 4.63% postgres postgres [.] slot_getattr
> + 3.69% postgres postgres [.] bpchareq
> + 3.39% postgres postgres [.] heap_getnext
> + 3.22% postgres postgres [.] float8pl
> + 2.86% postgres postgres [.]
> TupleHashTableMatch.isra.7
> + 2.77% postgres postgres [.] hashbpchar
> + 2.77% postgres postgres [.] float8mul
> + 2.73% postgres postgres [.] ExecAgg
> + 2.40% postgres postgres [.] hash_any
> + 2.34% postgres postgres [.]
> MemoryContextReset
> + 1.98% postgres postgres [.]
> pg_detoast_datum_packed
>
>
Our bottle neck is row format and row related processing.

> evalexpr90 is the expression that does the aggregate transition
> function. float8_accum, bpchareq, float8pl , float8mul, ... are all
> function calls, and a good percentage of the overhead in evalexpr90 is
> pushing arguments onto fcinfo->arg[nulls].
>
> Greetings,
>
> Andres Freund
>