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Oracle Core: Essential Internals for DBAs and Developers by Jonathan Lewis

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Commit SCN

Finally we come to the third linked list that runs through the undo records—the history of commit SCNs—and this is a topic that covers a lot of ground.

Earlier in this chapter I pointed out that when a transaction commits, it writes the current SCN into its transaction table slot, and that the redo change vector for this data block change constitutes the entirety of the so-called “commit record.”

Historically this was the only block change your session would make when committing a transaction, after which it would post a message to the log writer to copy the log buffer to disk and wait for the log writer to confirm that it had completed the write. The benefit of this approach (combined with the fact that the log writer would sit in ...

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