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From: David Johnston <[email protected]>
To: [email protected]
Subject: Re: MVCC snapshot timing
Date: Mon, 11 Nov 2013 19:25:59 -0800 (PST)
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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.




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