Re: [HACKERS] Re: Cursor with hold emits the same row more than once across commits in 8.3.7

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>, pgsql-bugs(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] Re: Cursor with hold emits the same row more than once across commits in 8.3.7
Date: 2009-06-09 18:33:18
Message-ID: 25190.1244572398@sss.pgh.pa.us
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Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Tue, 2009-06-09 at 10:51 -0700, Jeff Davis wrote:
>> I don't know what you mean by "frozen" exactly, but the start point of a
>> synchronized scan is stored in shared memory; otherwise, it wouldn't
>> know where to stop.

> Correction: I didn't actually mean _shared_ memory there. It's just
> backend-local memory.

Well, wherever it's stored, it's a demonstrable fact that we're not
getting the same rows after ExecutorRewind(); and that we do get the
same rows out if we disable synchronize_seqscans in Mark's test case.
I haven't got round to identifying exactly what to change if we decide
to go for a narrow fix instead of storing the query results at a higher
level.

regards, tom lane

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