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Home -> Community -> Mailing Lists -> Oracle-L -> Checkpoint queue
Yesterday I posted a response to a message about LRUW and checkpoint queue
list. I said I could find no mention of "checkpoint queue list" anywhere.
Today I'm re-reading R. Velpuri et al's Oracle8 Backup and Recovery Handbook (not the 8i edition). On pages 246-7, it talks about "checkpoint queue". This is the n-th time I read it and it finally makes sense. [note]
A little more research regarding thie queue. It appears that in 8i, only 8.1.5 has a Checkpoint queue, as seen from v$sgastat (or its fixed table x$ksmss). Beginning with 8.1.6, v$sgastat or x$ksmss does not have this entry. My wild guess is that since the checkpoint queue has a functionality so close to the write list of the buffer cache, maybe Oracle decided to use the write list to find dirty buffers to perform a checkpoint, without maintaining a separate list. This makes the difference fuzzier between the two functions of DBWRn, i.e., writing dirty buffers on request of server processes that need free buffers, and checkpointing. Again, this is my naive guess.
Yong Huang
yong321_at_yahoo.com
[note]
Except one point: Checkpoint works from the latest dirty buffers toward the
oldest according to the second bullet on p.247. But p.246 says DBWR writes out
the buffers in ascending, not descending, low redo order.
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