RE: Operations that perform multiblock I/O and cluster factor
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: <Josh.Collier@xxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 10 Dec 2007 12:55:07 -0700
I'm pretty sure you are correct - only FTS and FFS will perform "db file
scattered read" (reference:
http://download.oracle.com/docs/cd/B10501_01/server.920/a96533/instance_
tune.htm#15945). There are other multi-block I/Os though, for example
direct path reads & writes to temp, but those show up under their own
wait events, not "db file scattered read", and they do not occur on
behalf of an index range scan. I think your co-worker is wrong and if
s/he's going to make such claims in contradiction to the documentation -
the burden of proof is on him so ask him/her to show you a 10046 trace
file with "db file scattered read" wait events coming from an INDEX
RANGE SCAN, or some other proof.
Regards,
Brandon
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Josh Collier
Are there any other access paths that are served by multiblock I/O? My
co-worker contends: If the range scan is not a full scan, the query
optimizer will decide whether to use a scattered read depending on the
fraction of rows in the scan and the cluster factor of the index.
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