From: | "Etsuro Fujita" <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
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To: | "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "'PostgreSQL-development'" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Update obsolete text in indexam.sgml |
Date: | 2012-11-07 02:32:20 |
Message-ID: | 001b01cdbc90$1ce514a0$56af3de0$@lab.ntt.co.jp |
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> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> "Etsuro Fujita" <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> writes:
> > Agreed. However, I am concerned about the next comment in the current code:
>
> > /*
> > * Our generic assumption is that the index pages will be read
> > * sequentially, so they cost seq_page_cost each, not random_page_cost.
> > * ...
>
> > I think this assumption is completely wrong, which has given me a motivation
> to
> > propose a patch, though I am missing something.
>
> Mph. It's pretty hard to argue that it's wrong without considering a
> specific index implementation, which in practice would have a ton of
> other details that need to be accounted for here. I don't have a strong
> objection to changing the sample code to use random_page_cost instead,
> but I doubt it will help anybody one way or another.
To avoid creating unnecessary confusion among Index AM developers, I think it
would be better that the docs' sample code is consistent with the actual code in
selfuncs.c, which the docs referred to at the end of the page. No?
Thanks,
Best regards,
Etsuro Fujita
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