RE: db_file_multiblock_read_count causing full scans to take longer?
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: <don@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 19 Dec 2006 12:01:43 -0700
What version? What is your mbrc system stat?
Yes, the higher dbfmbrc should generally improve the speed of full
scans, that is assuming that it actually makes a difference in the
number of required I/O operations. Often the effective multiblock read
size isn't even close to your dbfmbrc setting due to some blocks already
being cached, extent boundaries, etc. Are you sure you have the exact
same plan for this query before and after the increase in dbfmbrc? Can
you share the plans, executions statistics and wait event summary (9i+)
from tkprof with both dbfmbrc settings? Be sure to run the trace with
WAITS and statistics_level=all.
Regards,
Brandon
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