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Re: Re: Postgres and Oracle differences and questions

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hannu Krosing <hannu(at)tm(dot)ee>
Cc: Jan Wieck <janwieck(at)Yahoo(dot)com>, "D(dot) Johnson" <dspectra(at)home(dot)com>, pgsql-interfaces(at)postgresql(dot)org
Subject: Re: Re: Postgres and Oracle differences and questions
Date: 2001-02-07 15:36:18
Message-ID: 28278.981560178@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-interfaces
Hannu Krosing <hannu(at)tm(dot)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

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