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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [BUG?] tuples from file_fdw has strange xids.
Date: 2014-07-16 15:10:06
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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.

regards, tom lane

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