Message-ID: <54DF9559.8080109@tbz-pariv.de>
Date: Sat, 14 Feb 2015 19:35:05 +0100
From: "Sven R. Kunze" <srkunze@tbz-pariv.de>
Organization: TBZ-PARIV GmbH
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-performance@postgresql.org
Subject: Re: Reverse Key Index
References: <54DF9036.8080502@tbz-pariv.de> <7978.1423937899@sss.pgh.pa.us>
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Thanks for the immediate reply.

I understand the use case is quite limited.

On the other hand, I see potential when it comes to applications which=20
use PostgreSQL. There, programmers would have to change a lot of code to=20
tweak existing (and more importantly working) queries to hash/reverse an=20
id column first. Using ORMs would make this change even more painful and=20
maybe even impossible.

When reading=20
https://richardfoote.wordpress.com/2008/01/14/introduction-to-reverse-key-i=
ndexes-part-i/=20
carefully, it also seems to work with index scan partially in case of=20
equality comparisons.


On 14.02.2015 19:18, Tom Lane wrote:
> "Sven R. Kunze" <srkunze@tbz-pariv.de> writes:
>> does PostgreSQL support the concept of reverse key indexing as described
>> here? I couldn't find any documentation on this yet.
>> http://www.toadworld.com/platforms/oracle/w/wiki/11075.reverse-key-index=
-from-the-concept-to-internals.aspx
> There's nothing built-in for that (and frankly, it doesn't sound useful
> enough that we'd ever add it).  You could get the effect easily enough
> with an expression index on a byte-reversing function.  A related thing
> that people often do is create an index on a hash function.
>
> 			regards, tom lane


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Sven R. Kunze
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Tel: +49 (0)371 33714721, Fax: +49 (0)371 5347920
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