Date: Fri, 3 Jan 2020 10:03:15 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: distinguish index cost component from table component
Message-ID: <20200103160315.GL12066@telsasoft.com>
References: <20200103141427.GK12066@telsasoft.com>
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On Fri, Jan 03, 2020 at 09:33:35AM -0500, Jeff Janes wrote:
> Of course this doesn't really answer your question, as the
> separately-reported costs of a bitmap heap and bitmap index scan are
> unlikely to match what the costs would be of a regular index scan, if they
> were reported separately.

I think the cost of index component of bitmap scan would be exactly the same
as the cost of the original indexscan.

>> Or maybe explain should report it.
> 
> I wouldn't be optimistic about getting such a backwards-incompatible change
> accepted (plus it would surely add some small accounting overhead, which
> again would probably not be acceptable). But if you do enough tuning work,
> perhaps it would be worth carrying an out-of-tree patch to implement that.
> I wouldn't be so interested in writing such a patch, but would be
> interested in using one were it available somewhere.

I did the attached in the simplest possible way.  If it's somehow possible get
the path's index_total_cost from the plan, then there'd be no additional
overhead.

Justin

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