What is foregraound and backgroup wait events?: Its *who* is doing the waiting that determines foreground or background. *You* run a query that does a full scan... its a *foreground* db file scattered read. *SMON* runs a query that a full scan... its a *background* db file scattered read, then there *might* be some interaction between the two, for example: *You* do a commit, its foreground wait for 'log file sync'. You've asked LGWR to write some data, so you have a foreground wait but you are waiting on a background process to complete. LGWR dispatches the I/O off to the OS and it is now waiting for the I/O to complete. So it has a background wait of "log file parallel write". You could argue that *you* are also effectively waiting on that as well, but we don't make that interpretation because it wasn't you that issued the I/O. Eventually the IO completes and LGWR is done, so its no longer waiting. Shortly thereafter, LGWR is going to let you know that t...
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