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I've been studying for the 9i OCP DBA tests. I passed the SQL test no
problem and now I'm on to the DBA Fundamentals I test. I really want to
understand what is physically going on during a transaction, but all the
books I have either contradict each other or do not fully explain what's
happening. If anyone wants to take a bit of their time to get a rookie off
to a good start, I'd greatly appreciate it. Here are a few questions:
Let's say we're doing an update statement. Please note where I'm wrong/confused/omit something important
I was trying to simplify this by thinking old data, new data, disk data, RAM data and figuring out which is which.
Old Data on Disk (DBF data files)
Old Data in RAM (first the buffer cache, then to the RollBack Segment)
New Data RAM (modified in buffer cache, then to Redo Log Cache)
New Data on Disk (LGWR writes redo log cache data to redo log files, DBWR
writes buffer cache data to DBF data files)
Do the redo log buffer, the rollback segment (or undo tablespace) all have a
copy of the old data?
Do the buffer cache and redo log cache both have copies of the changed data?
What the heck is undo? Is it the old data in RAM in the rollback segment?
Is the rollback segment in RAM in the SGA or the PGA?
If a rollback segment is in RAM and it's also in an UNDO tablespace on disk,
is it buffering to disk only if RAM runs out?
I've read 5 books on 9i and I'm getting close to the point of utter disgust that none of these books tell you what Oracle is doing. None of them. It's rediculous. I can't go into a job with a paper DBA certificate and not know what's happening inside the DB. Please someone help me (and I'm sure a lot of other confused people) understand a simple update statement. Thanks again...Paul Received on Wed Oct 23 2002 - 00:47:04 CDT