| From: | Peter Geoghegan <peter(at)2ndquadrant(dot)com> |
|---|---|
| To: | Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PG Hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: sortsupport for text |
| Date: | 2012-06-20 14:19:21 |
| Message-ID: | CAEYLb_WJ6i7tZqpYiD+DDNKbjuRsFY_6PRXmCm0h2r4CyEJ7fQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 20 June 2012 15:10, Greg Stark <stark(at)mit(dot)edu> wrote:
> On Sun, Jun 17, 2012 at 9:26 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The trick for hashing such datatypes is to be able to guarantee that
>> "equal" values hash to the same hash code, which is typically possible
>> as long as you know the equality rules well enough. We could possibly
>> do that for text with pure-strcoll equality if we knew all the details
>> of what strcoll would consider "equal", but we do not.
>
> It occurs to me that strxfrm would answer this question. If we made
> the hash function hash the result of strxfrm then we could make
> equality use strcoll and not fall back to strcmp.
What about per-column collations?
--
Peter Geoghegan http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services
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