LGWR improvement
According kevinclosson’s comments,and tom’s reply,Oracle improved LGWR work mechanism in 10g and it shortens “log file sync” wait event apparently.
Quote my understanding here,
in 8i the log writer checks the entire x$ array (process array) at the end of a log write to see which sessions have had their log sync request honoured. But in 9i the array is only checked up to its high-water mark.
while in 10g, LGWR can use wait&post(a semaphore operation) to notify waiting processes that their log entries were writeen to disk. Then noneed to scan every process slot in x$ array
It’s expected behavior that log file sync total wait time and average wait time decrease a little after upgrade.
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