From: Tom Lane <tgl@sss.pgh.pa.us>
To: zhangjinyu <beijing_pg@163.com>
cc: pgsql-bugs@postgresql.org, pgsql-docs@postgresql.org
Subject: Re: [BUGS] Re: BUG #13541: There is a visibility issue when run some
 DDL and Query. The time window is very shot
In-reply-to: <1439552734803-5862147.post@n5.nabble.com>
References: <20150807121643.32633.60549@wrigleys.postgresql.org>
 <CAJrrPGd--dTUoRpwiSmNVpa56sbCMMB-xB4=Qc4um1NNnt4uhQ@mail.gmail.com>
 <1439552734803-5862147.post@n5.nabble.com>
Comments: In-reply-to zhangjinyu <beijing_pg@163.com>
 message dated "Fri, 14 Aug 2015 04:45:34 -0700"
Date: Fri, 14 Aug 2015 10:23:10 -0400
Message-ID: <4140.1439562190@sss.pgh.pa.us>
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zhangjinyu <beijing_pg@163.com> writes:
> The DDL query(alter ...set data type ) rewrites all tuples with new
> transaction xid,  so if the transaction isolation level is repeatable read,
> that will cause wrong result.

Yes.  This is unlikely to change, but we ought to document it.

I see that we have documentation warning about this sort of effect in the
TRUNCATE reference page, but not in ALTER TABLE's.  Rather than
copy-and-paste that, ISTM it'd be better to move the warning to somewhere
in mvcc.sgml.

			regards, tom lane


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