RE: RE: should you seperate indexes from tables in seperate dataf

For a given statements execution, running in serial, you will not find an index and a table being accessed in parallel. Thus, there is no contention, for a given statement, between the tables and indexes accessed by that statement. Thus, one could argue the merits of not needing to seperate indexes and data in a low concurrency environment.

OTOH, high concurrency leads to hot blocks, which often leads to a requirement of distributing IO. In this case, seperating indexes and data may be one step in that direction.

RAID technologies, if properly configured, can eliminate some of the risk from co-location of data of course.... but in the end there is no substitute for carefully laid out data.

RF

-----Original Message-----
From: rgaffuri_at_cox.net
To: Multiple recipients of list ORACLE-L Sent: 7/15/2003 10:29 AM
Subject: Re: RE: should you seperate indexes from tables in seperate datafiles

does anyoen disagree? Didnt this get started with the 'DBA Handbook' or was it a different text?

>
> From: "Mercadante, Thomas F" <NDATFM_at_labor.state.ny.us>
> Date: 2003/07/15 Tue AM 11:10:05 EDT
> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> Subject: RE: should you seperate indexes from tables in seperate
datafiles
>
> R,
>
> Some of it depends on the disk storage. I have always followed the
> time-proven method of organizing disks and placing indexes away from
the
> tables they belong to.
>
> Our warehouse is using EMC external disk. What the warehouse
architect did
> was to stripe the EMC disks in such a way that all mount points (Sun
system)
> are spread across all the EMC disks. What this does is to spread all
files
> in the database across all the EMC drives. And with 4 Gig of EMC
cache
> available, it further disproves the theory that separing indexes from
data
> are required. The end result, in my case, is almost like one big RAM
disk -
> where all disk IO is spread across all disk.
>
> If you do not have this arrangement, then I would still try and keep
indexes
> and data away from each other. But let's face it, we *never* have
enough
> disk mount points, so we end up merging things together somewhat
anyway.
>
> hope this helps.
>
> Tom Mercadante
> Oracle Certified Professional
>
>
> -----Original Message-----
> Sent: Tuesday, July 15, 2003 10:49 AM
> To: Multiple recipients of list ORACLE-L
>
>
> There has been alot of literature stating that you will recieve
performance
> improvements by seperating indexes and tables across multiple I/O
points.
>
> Ie... you have a tables tablespace and an index tablespace. If you put
them
> on seperate hard drives, you will have less I/O contention.
>
> Now Im seeing some articles stating that this is not true. That oracle
> actually accesses indexes and tables serially. Now it might be useful
> seperate indexes from tables for maintenance purposes but this wont
lower
> I/O contention.
>
> Can anyone chime in on this? Curious to see where the evidence is
leading?
>
> --
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> Author: <rgaffuri_at_cox.net
> INET: rgaffuri_at_cox.net
>
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