From: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
---|---|
To: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: distinguish index cost component from table component |
Date: | 2020-01-03 16:03:15 |
Message-ID: | 20200103160315.GL12066@telsasoft.com |
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Lists: | pgsql-hackers pgsql-performance |
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
Attachment | Content-Type | Size |
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v1-0001-explain-show-index_total_cost.patch | text/x-diff | 1.9 KB |
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