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Re: What is the maximum encoding-conversion growth rate, anyway?

From: Tatsuo Ishii <ishii(at)postgresql(dot)org>
To: tgl(at)sss(dot)pgh(dot)pa(dot)us
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: What is the maximum encoding-conversion growth rate, anyway?
Date: 2007-05-29 02:49:00
Message-ID: 20070529.114900.23027278.t-ishii@sraoss.co.jp (view raw or flat)
Thread:
Lists: pgsql-hackers
> > Can we add a column to pg_conversion which represents the "growth
> > rate"? This would reduce the rate for most encodings much smaller than
> > 6.
> 
> We need to do something, but the pg_conversion catalog seems a bad place
> to put the info --- don't we have places that need to be able to do
> conversion without catalog access?

Can you tell me where? I thought conversion functions are always
called by using OidFunctionCall5 thus we need to consult the
pg_conversion catalog beforehand anyway.

> Perhaps better would be to redefine the API for the conversion functions
> so that they palloc their own result space.  Then each conversion
> function would have to know the maximum growth rate for its particular
> conversion.  This change would also make it feasible for a conversion
> function to prescan the data and determine an exact output size, if that
> seemed worthwhile because the potential growth rate was too extreme.
--
Tatsuo Ishii
SRA OSS, Inc. Japan

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