There are four conditions that cause LGWR to perform a redo write.
Note that commits within recursive calls (such as procedural code execute calls) do not need to sync their redo until a response is about to be returned to the user. Therefore recursive calls just sync the commit RBA of their most recent COMMIT upon return to the user call. They do not sync each commit.
An SGA variable (kcrfshsb, according to bug 182447) is used to communicate the log block number up to which the redo thread needs to be synced. If several commits occur in distinct transactions before LGWR wakes up, this variable records the highest log block number that needs to be synced, and the commit markers are all flushed to disk in a single redo write. This is sometimes called a group commit.
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05-Apr-2002 |
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