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Updates since the previous commit point Vs updates prior to the commit point

 
Greenhorn
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The quote below is from An Introduction to Database Systems, 8th edition, C J Date. I am confused since I think "all updates since the previous commit point" is the same as "updates Prior to the commit point". Am I wrong?

" all database updates made by the executing program since the previous commit point are committed; that is, they are made permanent, in the sense that they are guaranteed to be recorded in the database. Prior to the commit point , all such updates must be regarded as tentative only-tentative"
 
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'Since' means 'after' and 'prior to' means 'before'.
 
Tara Far
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Stephan van Hulst wrote:'Since' means 'after' and 'prior to' means 'before'.


Yes, I know. That is like this. The updates since the previous commit point are #1, #2 and #3. Also the updates before the commit point are #1, #2 and #3. So they are identical.

A(the previous commit point):

1:....
2:....
3:......

B(The commit point):
 
Stephan van Hulst
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No. By 'previous commit point' and 'commit point', they mean the same commit. So it's like:

Changes 1, 2 and 3 are permanent. 4, 5 and 6 are only temporary, unless you make a new commit point.
 
Tara Far
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Stephan van Hulst wrote:No. By 'previous commit point' and 'commit point', they mean the same commit. So it's like:

Changes 1, 2 and 3 are permanent. 4, 5 and 6 are only temporary, unless you make a new commit point.


Many thanks, yes I understand that it should be exactly as you've written but the text is ambiguous. Sorry that I ask again, but if both  'previous commit point' and 'commit point' are the same commit, why does he say "since the previous commit point"  and then he uses "prior to the commit point"?
 
Stephan van Hulst
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I'm not sure why this confuses you.

In the example I wrote, 'since' refers to the changes after the last commit, i.e. 4, 5 and 6. 'prior to' refers to the changes before the last commit, or 1, 2 and 3. Why do these words give you such pause?
 
Tara Far
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Stephan van Hulst wrote:I'm not sure why this confuses you.

In the example I wrote, 'since' refers to the changes after the last commit, i.e. 4, 5 and 6. 'prior to' refers to the changes before the last commit, or 1, 2 and 3. Why do these words give you such pause?


I understand what you explained and it perfectly make sense but the text that I quoted is different from what you say.    
 
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Tara Far wrote:I am confused since I think "all updates since the previous commit point" is the same as "updates Prior to the commit point". Am I wrong?

" all database updates made by the executing program since the previous commit point are committed; that is, they are made permanent, in the sense that they are guaranteed to be recorded in the database. Prior to the commit point , all such updates must be regarded as tentative only-tentative"



I see your problem, there is some ambiguity. But there is one interpretation of that text which makes complete sense and another interpretation which is confusing and wrong. I would suggest accepting the one which makes sense.
 
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