RE: Tables and indexes on different disks

All,
I've seen this in a newsgroup discussion. Please check out

http://groups.google.com/groups?hl=en&lr=&safe=off&ic=1&th=77e35d10c7f264e7& seekd=921282244#921282244

Message 3 in the thread is what I'd like to refer you to. Thanks
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~ Rich Gesler
Oracle DBA
<>< Saved By Grace
LifeStyle Furninshings International
(336) 878-7268
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~  

-----Original Message-----
Sent: Tuesday, March 13, 2001 1:00 PM
To: Multiple recipients of list ORACLE-L

Oh brother....

Ok, assuming you have a single read/write arm and one read/write head (which is the usual case), the arm has to go to the index location, read it, then go to the table location and read that. If you perform several reads, it's going to go back and forth between the index location and the table location. Having them on separate disks, and hence separate read/write heads minimizes the back and forth movement, because on head stays around the index, the other stays around the table. This movement, BTW, is quite time consuming, relatively speaking.

>>> zaschke_at_suas.cz 03/13/01 10:31AM >>> Hi all,

I've read an interesting section in Oracle Docu (Tuning I/O):

---
Separating Tables and Indexes

It is not necessary to separate a frequently used table from its index.
During the course of a transaction, the index is read first, and then
the table is read. Because these I/Os occur sequentially, the table and
index can be stored on the same disk without contention. 
---

Why do you then recommend to separate tables and indexes to different
disks?

Thanks
        Mike


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Author: Michal Zaschke
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Author: Gesler, Richard
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