Re: Re: Abbreviated keys for Numeric

On 28/01/15 06:29, Andrew Gierth wrote:
>>>>>> "Peter" == Peter Geoghegan <pg@heroku.com> writes:
>   Peter> What I find particularly interesting about this patch is that it
>   Peter> makes sorting numerics significantly faster than even sorting
>   Peter> float8 values,
>
> Played some more with this. Testing on some different gcc versions
> showed that the results were not consistent between versions; the latest
> I tried (4.9) showed float8 as somewhat faster, while 4.7 showed float8
> as slightly slower; the difference was all in the time of the float8
> case, the time for numeric was virtually the same.
>
> For one specific test query, taking the best time of multiple runs,
>
> float8:   gcc4.7 = 980ms, gcc4.9 = 833ms
> numeric:  gcc4.7 = 940ms, gcc4.9 = 920ms
>
> (vs. 650ms for bigint on either version)
>
> So honestly I think abbreviation for float8 is a complete red herring.
>
> Also, I couldn't get any detectable benefit from inlining
> DatumGetFloat8, though I may have to play more with that to be certain
> (above tests did not have any float8-related modifications at all, just
> the datum and numeric abbrevs patches).
>
Since gcc5.0 is due to be released in less than 3 months, it might be 
worth testing with that.


Cheers,
Gavin