Re: [BUG?] tuples from file_fdw has strange xids.

From: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
To: tgl(at)sss(dot)pgh(dot)pa(dot)us
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [BUG?] tuples from file_fdw has strange xids.
Date: 2014-07-17 05:42:58
Message-ID: 20140717.144258.211139452.horiguchi.kyotaro@lab.ntt.co.jp
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Hello, sorry, it's my bad.

> Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> writes:
> > Hello, I found that tuples come from file_fdw has strange xmin and xmax.
>
> file_fdw isn't documented to return anything useful for xmin/xmax/etc,
> so I don't find this surprising.
>
> > The patch attached fixes the header of materialized tuple to be
> > sane (2, 0) if the source slot was a virtual tuple in mechanism().
>
> I don't really think it's ForeignNext's place to be doing something
> about this. It seems like a useless expenditure of cycles. Besides,
> this fails to cover e.g. postgres_fdw, which is likewise unconcerned
> about what it returns for system columns other than ctid.

I somehow misunderstood that postgres_fdw returns (xmin, xmax) =
(2, 0) but I confirmed that xmin, xmax and citd seems insane.

I completely agree with you.

Thank you for giving response for the stupid story.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center

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