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Posted Thursday, August 21, 2008 5:51 PM
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Mark D Powell (8/21/2008)
But Booksonline also contains this quote "Log files do not contain pages; they contain a series of log records."

Blame MS not the author or question as I found the same section you did but I also found this


Hi Mark, I am not blaming the author, just wanted to note that the log also stores the boot page.
Just for additional confusion, check this info from BOL:
The format of log records and pages is not constrained to follow the format of data pages.
http://msdn.microsoft.com/en-us/library/ms190925(SQL.90).aspx

I "think" that the info from your quote is incorrect (but of course correctly quoted from BOL).
It might be possible that the log contains both, pages for the header information, and log records for the log data. Or maybe the log reords are actually stored in pages as well.

But MS only knows


Best Regards,
Chris Büttner
Post #557001
Posted Tuesday, August 26, 2008 6:23 AM
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Thanks guys, I learnt something new from your links...


Post #558794
Posted Tuesday, August 26, 2008 8:15 AM
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I think the problem is the first quote should really say "data pages". I do not think the internal format of the log uses "pages" but rather places the data, copy of pages, into log records. The line you reference about not having to use the data page format hints that the original format is not maintained hence the logs do not contain pages. Yet, you can find the term used in the manuals.

The real problem is terminology. Page and block are often used as synonyms Really, a page should refer to the size of the IO used in OS page sets and the term should not be used to describe the database logical structure size or IO block size. But the technical writers have a bad habit of intermixing terms and leaving out qualifying adjectives that would be very beneficial to us mere users of the software.

The Oracle manuals are not much different though the database itself does offer a log more visibility into its internal structures

We live and learn (hopefully).

-- Mark D Powell --








Post #558906
Posted Saturday, December 18, 2010 1:24 PM


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The somewhat contradictory MS documentation is a bit of a mess. Anyway, it seems clear that if you lose File 1 page 9 in a mirrored database you can't even recover that page from the mirror http://msdn.microsoft.com/en-us/library/bb677167.aspx using the built-in recovery mechanism included in mirroring, no can you recover it by any other shortcut means - your database is dead until full recovery is done by one means or another (effectively blowing the whoe database away and recovering it from backups or with snapshot replication from a working copy or some equivalent equivalent mechanism) - at least I'm not aware of any means of recovering that page from the log file, so even though it appears that there is a copy in the log file it doesn't seem to be very useful (I suppose you might be able to do something with a physical level disc editor, but that's way outside the scope of SQL).

Tom
Post #1036917
Posted Wednesday, March 30, 2011 6:39 PM
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Great question considering 64% of the answers were incorrect! I came across this issue a short while ago which jogged my memory for this question, but nice to know. Thanks
Post #1086582
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