Date: Mon, 11 Nov 2013 19:28:15 -0800 (PST)
From: David Johnston <polobo@yahoo.com>
To: pgsql-docs@postgresql.org
Message-ID: <1384226895502-5777854.post@n5.nabble.com>
In-Reply-To: <1384226759124-5777852.post@n5.nabble.com>
References: <20131111175737.GA15562@momjian.us>
 <13024.1384202385@sss.pgh.pa.us> <20131111205833.GC15562@momjian.us>
 <20331.1384221575@sss.pgh.pa.us> <20131112021954.GD15562@momjian.us>
 <21328.1384223235@sss.pgh.pa.us> <20131112024609.GG15562@momjian.us>
 <1384226759124-5777852.post@n5.nabble.com>
Subject: Re: MVCC snapshot timing
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Precedence: bulk
Sender: pgsql-docs-owner@postgresql.org

David Johnston wrote
> This reads badly to my ears:
>> This means that while querying a database each SQL statement sees a
>> snapshot of data (a database version) as it was some time ago, regardless
>> of the current state of the underlying data.
> How about something closer to:
>> This means for each SQL statement the user can specify a relative
>> point-in-time snapshot (database version) of the database against which
>> to query.  These snapshot options are 1) the most recent committed data
>> currently available database-wide - including implicit commits (see
>> note), or 2) the committed data as-of the beginning of the current
>> transaction - including any changes made in the same.
>> 
>> Note: an implicit commit occurs only within a multi-statement
>> transaction.  For the purpose of determining if data has been committed
>> any prior statements in the same transaction are deemed to have been
>> committed when viewed by later statements.
> I know this is an introduction paragraph so the broad concept is being
> focused on rather than how such a user would in fact make this choice.
>  
> I don't know that the term "implicit commit" is used elsewhere, likely
> not, but in effect that is what a statement in a transaction is seeing
> with respect to prior statements in the same transaction.  Naming this
> behavior in the introduction would allow for someone less verbose
> descriptions to be used in detail sections.
> 
> The above could be better integrated into the intro but I wanted to get
> opinions on the approach first.
> 
> David J.

So with the comment about implicit commits the phrase "including any changes
made in the same." can be dropped since that is what I was trying to imply
before I devised the new term.

David J.


--
View this message in context: http://postgresql.1045698.n5.nabble.com/MVCC-snapshot-timing-tp5777759p5777854.html
Sent from the PostgreSQL - docs mailing list archive at Nabble.com.


-- 
Sent via pgsql-docs mailing list (pgsql-docs@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-docs