Date: Mon, 11 Nov 2013 15:58:33 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL-documentation <pgsql-docs@postgresql.org>
Subject: Re: MVCC snapshot timing
Message-ID: <20131111205833.GC15562@momjian.us>
References: <20131111175737.GA15562@momjian.us>
 <13024.1384202385@sss.pgh.pa.us>
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On Mon, Nov 11, 2013 at 03:39:45PM -0500, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > I received a private email report that our introductory MVCC
> > documentation is unclear about when a snapshot is taken.  I have
> > adjusted the wording in the attached patch to be less precise about
> > snapshot timing. Snapshot timing is controlled by the session isolation
> > level, which I don't think we want to cover in this introductory
> > paragraph.
> 
> I'm not really seeing the point of s/transaction/session/ here.
> The phrasing is a bit awkward and maybe could be improved, but I think you
> should keep it referring to transactions.

Well, the problem with the original wording is that we don't take a new
snapshot for every transaction in the default read-committed mode. 
Would you prefer I refer to statements, e.g.:

     This means that while querying a database each statement sees

This is our default behavior.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +


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