Operations that perform multiblock I/O and cluster factor
- From: Josh Collier <Josh.Collier@xxxxxxxxxxxx>
- To: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 10 Dec 2007 11:14:49 -0800
Hi,
Having a bit of a debate with a peer. Perhaps you can help me.
Its my understanding that the only i/o operations that trigger multiblock I/O,
i.e. db file scattered read i/o that is influenced by the multi block read
count init parameter, are as follows
1. full table scan
2. index fast full scan
All other block access paths use db file sequential read, aka single block
reads from the disk.
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.
I'm very curious about this because there isn't clear documentation anywhere
about this.
Thanks,
Josh C.
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