| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Eisentraut <peter_e(at)gmx(dot)net>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Per-column collation, proof of concept |
| Date: | 2010-07-15 17:04:19 |
| Message-ID: | AANLkTikAXop_9dqQeVzC-NfeY0hpHTwCPjJPMTAsavmM@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Jul 15, 2010 at 4:24 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> The problem with not doing that is it breaks hashing --- hash joins and
> hash aggregation being the real pain points.
>
> citext works around this in a rather klugy fashion by decreeing that two
> strings are equal iff their str_tolower() conversions are bitwise equal.
> So it can hash the str_tolower() representation. But that's kinda slow
> and it fails in the general case anyhow, I think.
I think the general equivalent would be to call strxfrm and hash the
result of that.
--
greg
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