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      • 15. Re: when i start my hot backup my database getting very slow
        Jonathan Lewis
        jgarry wrote:
        Uwe Hesse wrote:
        It is very likely that you experience slow performance with ALTER DATABASE BEGIN BACKUP , because until you do ALTER DATABASE END BACKUP , every modified block is additionally written into the online logfiles .
        Doesn't that happen only the first time the block is modified?
        It's somewhere in between the two. Specifically, whenever the block is subject to a physical read into the buffer cache, the first change after that results in the whole block being copied into the redo before the change vector is copied.

        Jonathan Lewis
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