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:
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.
