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Operations that perform multiblock I/O and cluster factor

From: Josh Collier <Josh.Collier_at_banfield.net>
Date: Mon, 10 Dec 2007 11:14:49 -0800
Message-ID: <578806DDE66A3A45916740EB73C6982AB42BB5D391@M1EXCHANGE01.mmi.local>


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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Received on Mon Dec 10 2007 - 13:14:49 CST

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