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From Mike Matrigali <mikem_...@sbcglobal.net>
Subject Re: Derby architecture/design documents
Date Mon, 07 Feb 2005 19:25:12 GMT
The page version number is stored in both the in memory and on disk
version of the page.

It is definitely possible for changes to pages to be written to disk
before the changes are committed, but not before the log records
describing the changes to the pages have been forced to disk.  As you
say, the most likely cause for this is a the page cache becoming full.

RPost wrote:

>>"Dibyendu Majumdar" wrote:
> 
> 
>>Although Derby uses LogInstant, it does not save this with the page data.
> 
> Instead, a page version >number is stored. The page version number is also
> stored in the log records associated with the page
> 
> Mike's comments "As you say in derby all the log records are associated with
> a page, and thus have a page version number. That page version number in the
> log is compared with the page version number of the page during redo to
> determine if the log record needs to be applied."
> 
> Does this mean that the page number is stored both in the 'in memory' image
> of the page and also in the version of the page written to disk?
> 
> Are changes to pages ever written to disk before the changes are actually
> committed? For example, if the page cache is full?
> 
> 
> 

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