Re: 9.5 release notes

On Sat, Jun 13, 2015 at 3:53 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> I think we should really address this. Attached patch adds a new
> release note item for it. It also adds to the documentation that
> explains why users should prefer varchar(n)/text to character(n); the
> lack of abbreviated key support now becomes a huge disadvantage for
> character(n), whereas in previous versions the disadvantages were
> fairly minor.
>
> In passing, I updated the existing sort item to reflect that only
> varchar(n), text, and numeric benefit from the abbreviation
> optimization (not character types more generally + numeric), and added
> a note on the effectiveness of the abbreviation optimization alone.

A recent e-mail from Kaigai-san [1] reminded me of this item. I really
think this limitation of char(n) needs to be documented along the
lines I proposed here back in June. Benchmarks like TPC-H use char(n)
extensively, since it's faster in other systems. However, PostgreSQL
now has hugely inferior sort performance for that type as compared to
text/varchar(n). This needs to be highlighted.

[1] http://www.postgresql.org/message-id/flat/CAM3SWZRRCs6KAyN-bDsh0_pG=8xm3fvcF1X9dLsVd3wVbt1pHw(at)mail(dot)gmail(dot)com#CAM3SWZRRCs6KAyN-bDsh0_pG=8xm3fvcF1X9dLsVd3wVbt1pHw@mail.gmail.com
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Peter Geoghegan