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The Page Checksum

  • April 10, 2011 at 1:35 am

    #63855

    Comments posted to this topic are about the item The Page Checksum

  • April 10, 2011 at 1:36 am

    #1309591

    Thanks for a good question.

    M&M

  • April 10, 2011 at 11:35 pm

    #1309658

    Thanks for the question!

  • April 10, 2011 at 11:51 pm

    #1309670

    Great question, thanks.

    Need an answer? No, you need a question
    My blog at https://sqlkover.com.
    MCSE Business Intelligence - Microsoft Data Platform MVP

  • April 11, 2011 at 3:02 am

    #1309704

    Thanks for the question learnt something new today 🙂

  • April 11, 2011 at 8:25 am

    #1309844

    Good question.

  • April 11, 2011 at 9:03 am

    #1309879

    Maybe my reading comprehension is off this morning, but it seems that, according to the link specified, both of the last two options are correct:

    When CHECKSUM is enabled for the PAGE_VERIFY database option, the SQL Server Database Engine calculates a checksum over the contents of the whole page, and stores the value in the page header when a page is written to disk. When the page is read from disk, the checksum is recomputed and compared to the checksum value that is stored in the page header.

    So I'm reading this as "the engine calculates the checksum and stores that value when the page is written to disk, and then recalculates the checksum every time the page is read to verify the integrity of the page." If this is true, it seems to me that the checksum of the page is calculated and stored when the page is written, and calculated and compared when the page is read. But both operations are calculating the checksum.

    But maybe my non-caffienated brain is missing something...

  • April 11, 2011 at 9:09 am

    #1309885

    Read the question as 'when is it first computed', since there's mention of changing the page verify. Basically, when is the checksum added to a page. It won't be checked (on read) if the page doesn't have one when it's read in.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • April 11, 2011 at 11:25 am

    #1309979

    I did not KNOW the answer but I deduced it by using what I already know about physical storage. The answer makes sense and I am glad you made me think about it.

    Peter Trast
    Microsoft Certified ...(insert many literal strings here)
    Microsoft Design Architect with Alexander Open Systems

  • April 11, 2011 at 3:21 pm

    #1310135

    Nice question. Thanks

    Jason...AKA CirqueDeSQLeil
    _______________________________________________
    I have given a name to my pain...MCM SQL Server, MVP
    SQL RNNR
    Posting Performance Based Questions - Gail Shaw[/url]
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  • July 6, 2011 at 10:42 pm

    #1349418

    [font="Times New Roman"]

    Nice question!!

    [/font]

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