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Oracle Tips by Burleson |
Disk Contention
Once DBWR has been tuned, the DBA needs to
look at disk contention. Disk contention happens when one or more
users attempt to read the same disk at the same time, or in some
cases, access a different disk through the same controller path at
the same time. Spreading Oracle-related files across several
platters or sets of platters--the more the better--prevents this.
The new RAID options don’t relieve the DBA of file placement
concerns. You should be sure that the RAID volumes are properly set.
I had one system where a system administrator set up multiple RAID5
volumes using two disks for each volume (a hint: the 5 is a
meaningful number for RAID5).
The report in Source 13.17 can be used to
monitor relative-fill I/O efficiency--essentially, how many reads
are being performed per request as a percent. The more times the
process has to access the same datafile to get the same information,
the less efficient the datafile is. This could be caused by
colocation of indexes and tables, a poorly ordered table that is
scanned frequently, or having temporary or undo segments in with
data or index segments.
See Code Depot
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