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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Fujii Masao <masao.fujii@gmail.com>
cc: Andres Freund <andres@anarazel.de>,
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Subject: Re: WAL logging problem in 9.4.3?
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Comments: In-reply-to Fujii Masao <masao.fujii@gmail.com>
 message dated "Fri, 10 Jul 2015 01:52:36 +0900"
Date: Thu, 09 Jul 2015 13:27:43 -0400
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Fujii Masao <masao.fujii@gmail.com> writes:
> On Tue, Jul 7, 2015 at 12:49 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> One idea I had was to allow the COPY optimization only if the heap file is
>> physically zero-length at the time the COPY starts.

> This seems not helpful for the case where TRUNCATE is executed
> before COPY. No?

Huh?  The heap file would be zero length in that case.

> So, if COPY is executed multiple times at the same transaction,
> only first COPY can be optimized?

This is true, and I don't think we should care, especially not if we're
going to take risks of incorrect behavior in order to optimize that
third-order case.  The fact that we're dealing with this bug at all should
remind us that this stuff is harder than it looks.  I want a simple,
reliable, back-patchable fix, and I do not believe that what you are
suggesting would be any of those.

			regards, tom lane


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