To: Scott Cain <cain@cshl.org>
Cc: PgSQL Performance ML <pgsql-performance@postgresql.org>,
	pgsql-sql@postgresql.org
Subject: Re: [SQL] EXTERNAL storage and substring on long strings 
In-reply-to: <1060010735.1433.26.camel@localhost.localdomain> 
References: <1059679600.1429.41.camel@localhost.localdomain>
	<3F297CBA.1080703@joeconway.com> <1059686498.7505.558.camel@haggis>
	<1060010735.1433.26.camel@localhost.localdomain>
Comments: In-reply-to Scott Cain <cain@cshl.org>
	message dated "04 Aug 2003 11:25:36 -0400"
Date: Mon, 04 Aug 2003 11:53:43 -0400
Message-ID: <3574.1060012423@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Scott Cain <cain@cshl.org> writes:
> At least this appears to work and is much faster, completing substring
> operations like above in about 0.27 secs (that's about two orders of
> magnitude improvement!)

I find it really, really hard to believe that a crude reimplementation
in plpgsql of the TOAST concept could beat the built-in implementation
at all, let alone beat it by two orders of magnitude.

Either there's something unrealistic about your testing of the
dna_string function, or your original tests are not causing TOAST to be
invoked in the expected way, or there's a bug we need to fix.  I'd
really like to see some profiling of the poor-performing
external-storage case, so we can figure out what's going on.

			regards, tom lane