Re: Commit -> write to data file immediately???

David <david_petit_at_yahoo.com> wrote:
>Hi all,
>
> When user issues "commit", does Oracle writes all changed data (of
>this user) to data file immediately? Or Oracle writes to data file only
>when database buffer is full or during checkpoint? IF Oracle not writing
>to data file immediately, and at that time, Oracle is crashed and log
>files (all) are corrupted, how does Oracle to recover the "committed"
>data?

A commit will cause the redo log to be written to disk, but not the table data. DBWR will write table data to disk basically when it feels like it, or rather under one of a number of conditions it will wake up and under another set of conditions it will decide that it needs to do some work.

Redo is there to recover a consistent state after a failure. If there's an unexpected system failure, *and* your redo is corrupt, you in trouble. This is of course why all your logs are written to at least two seperate disks.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/