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From: David Johnston <[email protected]>
To: [email protected]
Subject: Re: MVCC snapshot timing
Date: Mon, 11 Nov 2013 19:28:15 -0800 (PST)
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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.




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