To: Hannu Krosing <hannu@tm.ee>
cc: Jan Wieck <janwieck@Yahoo.com>, "D. Johnson" <dspectra@home.com>,
	pgsql-interfaces@postgresql.org
Subject: Re: Re: Postgres and Oracle differences and questions 
In-reply-to: <3A8155DF.80007@tm.ee> 
References: <200102071006.FAA02488@jupiter.greatbridge.com>
	<3A8155DF.80007@tm.ee>
Comments: In-reply-to Hannu Krosing <hannu@tm.ee>
	message dated "Wed, 07 Feb 2001 16:04:15 +0200"
Date: Wed, 07 Feb 2001 10:36:18 -0500
Message-ID: <28278.981560178@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Hannu Krosing <hannu@tm.ee> writes:
> What are the performance implications - is it 1.01,  10 or 1000 times 
> slower than accessing the same file from fs for files in the range of 
> typical Office documents (0.2-20M) ?

I think that's a meaningless question unless you specify a particular
usage pattern --- but in any case, I doubt anyone has tried to
characterize it that way.  Feel free to run some experiments and tell
us about your results...

> Will updating one non-toasted field in a tuple copy the toasted one
> as well, or is only the reference copied ?

It copies the reference, see toast_insert_or_update in
src/backend/access/heap/tuptoaster.c.

Speaking of which, though, it looks like an update or insert will
forcibly uncompress (and later recompress) a compressed-in-line datum,
which seems like a waste of cycles to me.  Jan, shouldn't the test for
VARATT_IS_EXTENDED at line 357 instead read VARATT_IS_EXTERNAL?

			regards, tom lane