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All the Perl that's Practical to Extract and Report

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  • Fred and Mary start with:

    1 A
    2 B
    3 C

    Fred starts a transaction and updates the first two rows so the table that looks like:

    1 X
    2 Y
    3 C

    In the mean time Mary has started and finished a transaction that updates the third row:

    1 A
    2 B
    3 Z

    which means that Fred is seeing the "old" version of row three, and the table as a whole reflects something that will never have existed in the database.

    Make sense?

    • Oh! I replied to Aristotle without thinking too carefully about your reply. I can see how this could occur, but it's problematic because then things aren't atomic. If you take actions based upon this, you can still corrupt your data. You update row 3 because 'C' is there, but it's really not. Now you have a race condition because consistent reads aren't. Or did I misunderstand something?