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Don Burleson Blog 









Oracle - large or small data files sizing?

Oracle Database Tips by Donald Burleson

Question:  I just moved to a 64-bit server and I want to know if I should make large Oracle data files (greater then 2 gigabytes).  Also, is this a good policy of having 4 - 1GB datafiles OR its good to have 1 datafile of 4GB?

Answer:  Like the answer to all Oracle questions, it depends. If you have four disks, and this data file has a very read/write rate, then striping the files across the 4 disks can relieve I/O contention.

Creating large data files on a single disk spindle can cause high I/O latency, especially when:

  • The table spans multiple cylinders (requiring read-write head movement).
  • Multiple hot spots exist on different cylinders on the disk for the same file.

If you don't have multiple disks it's a moot issue, and I really detest some of the 144 gig disks because they shake like an out-of-balance washing machine when I/O rates get high and the read-write heads scream back-and-forth attempting to service all the data requests. 

Disk enqueues can occur when the disk is unable to quickly service concurrent requests.  Super-large disks can be problematic, and the most popular Oracle data files can be placed on the middle absolute track of the device to minimize read-write head movement.

For more on Oracle file sizing and disk I/O tuning, see these books:

- Oracle Tuning: The Definitive Reference

- Oracle Disk I/O Tuning

If you like Oracle tuning, you may enjoy my new book "Oracle Tuning: The Definitive Reference", over 900 pages of my favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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