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Re: [HACKERS] Performance testing of COPY (SELECT) TO

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Hans-Juergen Schoenig <postgres(at)cybertec(dot)at>
Cc: Zoltan Boszormenyi <zboszor(at)dunaweb(dot)hu>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] Performance testing of COPY (SELECT) TO
Date: 2006-08-28 16:13:15
Message-ID: 20060828161315.GM27526@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Hans-Juergen Schoenig wrote:
> 
> >Remember that we were talking about supporting views, not tables.  And
> >if a view uses a slow query then you are in immediate danger of having a
> >slow COPY.  This may not be a problem but it needs to be discussed and
> >an agreement must be reached before introducing such a change (and not
> >during feature freeze).
> 
> this will definitely be the case - however, this is not what it was made 
> for. it has not been made to be fast but it has been made to fulfill 
> some other task. the reason why this has been implemented is: consider a 
> large scale database containing hundreds of gigs of data. in our special 
> case we have to export in a flexible way. the data which has to be 
> exported comes from multiple tables (between 3 and 7 depending on the 
> data we are looking at in this project. the export has to be performed 
> in a flexible way and it needs certain parameters. defining tmp tables 
> and store the data in there is simply not "nice" at all. in most cases 
> exports want to transform data on the fly - speed is not as important as 
> flexibility here.

My question is, if we allow this:

copy (select * from view) to stdout;

(or to a file, whatever), is it enough for you?  Or would you insist on
also having

copy view to stdout;
?

We can, and the posted patch does, support the first form, but not the
second.  In fact I deliberately removed support for the second form for
Zoltán's patch because it uglifies the surrounding code.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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