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Full backup Scenario Expand / Collapse
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Posted Wednesday, March 31, 2010 8:38 AM


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Paul White NZ (3/31/2010)
Thank you, Peter. Of course, there are some edge cases and subtleties, but unless Mr Randal appears and tells me I know nothing about nothing...I'm happy with it.


I don't sweat the exceptions. Concepts first, exceptions later. Can't understand the exceptions until the normal process makes sense. I get grief for using broken analogies to explain concepts like joins but the students like simple explanations, even if they are flawed by real world applications.


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Post #893833
Posted Wednesday, March 31, 2010 2:58 PM


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Paul White NZ (3/31/2010)

The whole backup operation is conceptually quite simple:

    Force a database checkpoint (flush all updated-in-memory pages to disk before anything is read by the backup)

    Record the minimum recovery LSN (LSN1)

    Database data read begins

    Database data read ends

    Record the current LSN (LSN2)

    Read the transaction log from LSN1 to LSN2

Thanks Paul, that's a very clear description. It answers all the questions I had about whether dirty data is flushed first, when the start LSN is recorded, and whether the final LSN is allowed to be later than the current LSN at the end of the DB read.

And I see the MS design does include flushing already dirty pages to disc despite Hugo's suggestion that this is not a useful thing to do.



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Post #894230
Posted Wednesday, March 31, 2010 4:08 PM


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Tom.Thomson (3/31/2010)
And I see the MS design does include flushing already dirty pages to disc despite Hugo's suggestion that this is not a useful thing to do.

Yes, I noticed that as well. And was a bit surprised by it.

I'm glad Paul was able to find and post such a detailed description of the process. Thanks, Paul!



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Post #894272
Posted Thursday, April 1, 2010 3:33 AM


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Thanks, everyone. Glad I am not the only one to find this whole area fascinating.



Paul White
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Post #894538
Posted Thursday, April 1, 2010 9:47 AM
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Paul White NZ (4/1/2010)
Thanks, everyone. Glad I am not the only one to find this whole area fascinating.


Yes, I do too [for reasons unfathomable]

And I'm glad I kinda kicked off the discussion about when the backup knew when to stop. I'm slogging my way through all of Paul's postings, and drawing diagrams of my own.

Again, thanks to all.




Post #894957
Posted Thursday, June 10, 2010 3:46 AM
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Good question! Tests ones' understanding in a better ways.

Kudos to the Question submitter!
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