Re: WIP: Make timestamptz_out less slow.
| От | David Rowley |
|---|---|
| Тема | Re: WIP: Make timestamptz_out less slow. |
| Дата | |
| Msg-id | CAKJS1f_05cz-4_TsFPxCdnZpqOsNgLJxAsNq=s18K70jX6Cm+g@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: WIP: Make timestamptz_out less slow. (Alvaro Herrera <alvherre@2ndquadrant.com>) |
| Ответы |
Re: WIP: Make timestamptz_out less slow.
|
| Список | pgsql-hackers |
On 15 September 2015 at 05:52, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
Jim Nasby wrote:
> On 9/13/15 2:43 AM, David Rowley wrote:
> >Are you worried about this because I've not focused on optimising float
> >timestamps as much as int64 timestamps? Are there many people compiling
> >with float timestamps in the real world?
>
> My $0.02: the default was changed some 5 years ago so FP time is probably
> pretty rare now.
The default was FP for 8.3 and was changed before 8.4. Anybody who was
running with the default back then and who has pg_upgraded all the way
to current releases is still using floating-point date/times.
> I don't think it's worth a bunch of extra work to speed them up.
Not sure about that.
It's not like nothing is improved in float timestamps with this patch, it's only appending the non-zero fractional seconds that I've left alone. Every other portion of the timestamp has been improved.
I made a quick test as a demo. This is compiled with float timestamps.
create table ts (ts timestamp not null);
insert into ts select generate_series('2010-01-01 00:00:00', '2011-01-01 00:00:00', '1 sec'::interval);
vacuum freeze ts;
create table ts2 (ts timestamp not null);
insert into ts2 select generate_series('2010-01-01 00:00:00', '2010-01-01 00:00:31.536001', '1 microsecond'::interval);
vacuum freeze ts2;
Master:
copy ts to '/dev/null'; -- Test 1
Time: 18252.128 ms
Time: 18230.650 ms
Time: 18247.622 ms
copy ts2 to '/dev/null'; -- Test 2
Time: 30928.999 ms
Time: 30973.576 ms
Time: 30935.489 ms
Patched
copy ts to '/dev/null'; -- Test 1 (247%)
Time: 7378.243 ms
Time: 7383.486 ms
Time: 7385.675 ms
copy ts2 to '/dev/null'; -- Test 2 (142%)
Time: 21761.047 ms
Time: 21757.026 ms
Time: 21759.621 ms
The patched difference between ts and ts2 can be accounted for by the fact that I didn't find a better way to do:
if (fillzeros)
sprintf(cp, "%0*.*f", precision + 3, precision, fabs(sec + fsec));
else
sprintf(cp, "%.*f", precision, fabs(sec + fsec));
A fast path exists when the fractional seconds is zero, which is why there's such a variation between the 2 tests.
I did, however spend some time a few weekends ago writing a function to improve this, which is more aimed at improving poor performance of float4out and float8out. It's quite likely if I can get finished one day, it can help improve this case too.
Regards
David Rowley
--
David Rowley http://www.2ndQuadrant.com/
David Rowley http://www.2ndQuadrant.com/
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