RE: How are ITL entries banked?
- From: Rajesh Rao <Rajesh.Rao@xxxxxxxxxxxx>
- To: "vit.spinka@xxxxxxxxxxxx" <vit.spinka@xxxxxxxxxxxx>, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 8 Jan 2010 12:23:46 -0500
“ITL is blanked by the DML session only if the block is still in the cache”.
Doesn’t it work in conjunction with a parameter that defines the dirty block
threshold?
Regards
Raj
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of vit.spinka
Sent: Friday, January 08, 2010 12:01 PM
To: oracle-l@xxxxxxxxxxxxx
Cc: Martin.Klier@xxxxxxxxxx
Subject: Re: How are ITL entries banked?
Hi Martin,
the acutal algortihm is in fact a bit complicated; if I simplify it, then the
ITL is blanked by the DML session only if the block is still in the cache. This
is the "fast commit" cleanout.
If it's already on the disk, than it's blanked by any other session that reads
it from the disk next time. The session checks the undo if the referenced XID
is till active; if not, the commit SCN of that XID is used to blank the ITL. If
the XID is no longer in undo, we can safely assume the transaction already
commited and blank the ITL as well (using lowest SCN of any active
transaction). This is the "delayed block cleanout".
Note that blanking the ITL also involves setting the commit SCN of that
particular row, so we can properly answer any read-consistent queries.
Further details are described at http://www.jlcomp.demon.co.uk/cleanout.html .
Vit Spinka
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