Re: Abbreviated keys for Numeric (was: Re: B-Tree support function number 3 (strxfrm() optimization))

On 21.2.2015 00:14, Peter Geoghegan wrote:
> On Fri, Feb 20, 2015 at 1:33 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> For example with the same percentile_disc() test as in the other
>> thread:
>>
>> create table stuff as select random()::numeric as randnum from
>> generate_series(1,1000000);
>>
>> analyze stuff;
>>
>> select percentile_disc(0) within group (order by randnum) from
>> stuff;
>>
>>
>> I get pretty much no difference in runtimes (not even for the
>> smallest dataset, where the Datum patch speedup was significant).
>>
>> What am I doing wrong?
>
> So you're testing both the patches (numeric + datum tuplesort) at the
> same time?

No, I was just testing two similar patches separately. I.e. master vs.
each patch separately.

> I can't think why this would make any difference. Did you forget to
> initdb, so that the numeric sortsupport routine was used?

No, but just to be sure I repeated the benchmarks and I still get the
same results. Each test run does this:

1) remove data directory
2) initdb
3) copy postgresql.conf (with minor tweaks - work_mem/shared_buffers)
4) start
5) create database
6) create test table
7) run a query 5x

I repeated this, just to be sure, but nope - still no speedup :-(

For master vs. patch, I do get these results:

master patched speedup
---------------------------------------------------------
generate_series(1,1000000) 1.20 1.25 0.96
generate_series(1,2000000) 2.75 2.75 1.00
generate_series(1,3000000) 4.40 4.40 1.00

So, no difference :(

Scripts attached, but it's really trivial test - hopefully I haven't
done anything dumb.

--
Tomas Vondra http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services