RE: Ghost Data
Date: Tue, 30 Jun 2009 19:13:36 -0400
I'm sure someone else will actually *know* the answer, but I'll hazard a guess. I suspect that you're right, that it just grabs a full block worth of data from memory, before it writes it out. Perhaps they think it's better to do that than to write an unaligned block?
From: oracle-l-bounce_at_freelists.org on behalf of Allen, Brandon Sent: Tue 6/30/2009 6:41 PM
To: michaelw436_at_gmail.com; oracle-l
Subject: Ghost Data
I'm starting a new thread on this specific topic to avoid high jacking the other one. Reading about this "ghost data" reminds me of a surprising discovery I made a few months ago but had forgotten about until today.
I created a brand new tablespace with a new datafile, created one table in the new tablespace and inserted one row. When I ran "strings" on the datafile, I only saw the instance name and tablespace name - so far, so good. Then I forced a checkpoint to write the data out to the file and was surprised to find that when I looked at the datafile with "strings" again, it had a bunch of data from other database tables in it.
Is this normal, known behavior? Does Oracle just copy data from other blocks of the database into the new file as buffer space to fill it up? I duplicated this on 18.104.22.168 and 10.2.0.4.
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Michael Wehrle
Sent: Tuesday, June 30, 2009 1:45 PM
To: Mathias Magnusson; oracle-l
Subject: Re: Quickest Way To Recreate a Database
Mathias, Oracle explains what this ghost data is here...
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http://www.freelists.org/webpage/oracle-l Received on Tue Jun 30 2009 - 18:13:36 CDT