Re: About "Our CLUSTER implementation is pessimal" patch

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: Leonardo F <m_lists(at)yahoo(dot)it>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: About "Our CLUSTER implementation is pessimal" patch
Date: 2010-01-21 15:30:09
Message-ID: 7942.1264087809@sss.pgh.pa.us
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Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> writes:
> * I'd prefer to separate cost calculation routines from create_index_path()
> and cost_sort(), rather than using a dummy planner.

Don't go that way. The cost functions have enough dependencies on
low-level planner functionality that making them be standalone would be
a serious mess, both immediately and in terms of future maintenance.
(As an example, someday we'll probably get around to having cost_sort
actually look at the specific columns being sorted by, and that's
going to involve a lot of interaction with pathkeys.)

What I do think is that the quoted code snippet has no business being
outside the planner proper. It'd be better to put it in planner.c
or someplace like that.

regards, tom lane

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