Message-ID: <42D3217C.20703@arbash-meinel.com>
Date: Mon, 11 Jul 2005 20:48:44 -0500
From: John A Meinel <john@arbash-meinel.com>
User-Agent: Mozilla Thunderbird 1.0.2 (Macintosh/20050317)
MIME-Version: 1.0
To: Chris Travers <chris@metatrontech.com>,
	Postgresql Performance <pgsql-performance@postgresql.org>
Subject: Re: Sorting on longer key is faster ?
References: <20050709183842.2EABF52820@svr1.postgresql.org>
	<42D303CA.2020808@arbash-meinel.com>
	<42D31613.5020608@metatrontech.com>
In-Reply-To: <42D31613.5020608@metatrontech.com>
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature";
	boundary="------------enigEDC246B45A7210D61FBECEB2"

This is an OpenPGP/MIME signed message (RFC 2440 and 3156)
--------------enigEDC246B45A7210D61FBECEB2
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

Chris Travers wrote:
> John A Meinel wrote:
>
>> jobapply wrote:
>>
>>
>>> The 2 queries are almost same, but ORDER BY x||t is FASTER than ORDER
>>> BY x..
>>>
>>> How can that be possible?
>>>
>>> Btw: x and x||t are same ordered
>>>
>>> phoeniks=> explain analyze SELECT * FROM test WHERE i<20 ORDER BY x
>>> || t;
>>>                                                        QUERY PLAN
>>>
>>>
>>
>>
>> What types are x and t, I have the feeling "x || t" is actually a
>> boolean, so it is only a True/False sort, while ORDER BY x has to do
>> some sort of string comparison (which might actually be a locale
>> depended comparison, and strcoll can be very slow on some locales)
>>
>>
>>
> Am I reading this that wrong?  I would think that x || t would mean
> "concatenate x  and t."

Sorry, I think you are right. I was getting my operators mixed up.
>
> This is interesting.  I never through of writing a multicolumn sort this
> way....

I'm also surprised that the sort is faster with a merge operation. Are
you using UNICODE as the database format? I'm just wondering if it is
doing something funny like casting it to an easier to sort type.

>
> Best Wishes,
> Chris Travers
> Metatron Technology Consulting

PS> Don't forget to Reply All so that your messages go back to the list.

--------------enigEDC246B45A7210D61FBECEB2
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.0 (Darwin)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

iD8DBQFC0yF8JdeBCYSNAAMRAuLoAKCQRpqH4VQrgX1WYAPsdIkhvTGsIgCcDIsH
X59AVC17LTtLbpt8i6BHxaw=
=L2PD
-----END PGP SIGNATURE-----

--------------enigEDC246B45A7210D61FBECEB2--