Re: [BUGS] BUG #14505: explain verbose for postgresql_fdw

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От Jeff Janes
Тема Re: [BUGS] BUG #14505: explain verbose for postgresql_fdw
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Msg-id CAMkU=1z1H0v_9JTMVVqS3Z8mNnY-VSW2WOrOgQ+w42YQ1LC8Vw@mail.gmail.com
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Ответ на Re: [BUGS] BUG #14505: explain verbose for postgresql_fdw  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: [BUGS] BUG #14505: explain verbose for postgresql_fdw  (Tom Lane <tgl@sss.pgh.pa.us>)
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On Wed, Jan 18, 2017 at 5:27 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
jeff.janes@gmail.com writes:
> The "Output:" line of explain verbose lists columns of foreign table that
> are not actually output, or at least ought not be output.

That's an optimization to avoid an unnecessary projection step.  It has
nothing to do with what's retrieved from the remote, and for that matter
it's not specific to foreign tables.

Is all of that data actually being transferred from the foreign to the local?  If so, I don't think the optimization is a good choice in this case.  Do you know where can I find the relevant source code which decides on this?
 
Cheers,

Jeff

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