Re: good value for optimizer_index_cost_adj

Well, Tim did say he was making a long story short.

    scattered reads = multiblock reads which are typically     associated with tablescans, but can be index fast full     scans.

    sequential reads = single block reads which are typically     associated with index block reads, table blocks accessed     as a consequence of index block reads, but can be     one-off blocks in table scans and index fast full scans     due to the existence of previously buffered blocks or     tail-end blocks on extents.

And then there are cached LOB reads and ....

Jonathan Lewis
http://www.jlcomp.demon.co.uk

Author of:
Practical Oracle 8i: Building Efficient Databases

Next Seminar - Australia - July/August
http://www.jlcomp.demon.co.uk/seminar.html

Host to The Co-Operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 25 April 2002 00:21

|> "db file scattered read" (associated with FULL
|> table scans) and "db file sequential
|> read" (associated with indexed scans)
|
|But see, Tuning 101, p. 35, where a "db file sequential read" is
|investigated and the waits are found to be reads from a *table*.
|
|And other examples elsewhere, where "db file scattered read" is found
to be
|associated with reads from an index.
|

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