Re: should you seperate indexes from tables in seperate datafiles?

Hi!

There's not just head movement involved, there is disk rotational latency as well, and you have to cope with it whether even if your disk reading heads are in the same place.

But more importantly, as Rachel already stated, that if you got multi-user environment (as a usual Oracle environment is), then you won't get no real benefit from separating data & indexes on different disks, because disk heads will never be there where you leave them, there's always someone else who wants to read or write something.

Tanel.

• Original Message ----- From: "Garry Gillies" <g.gillies_at_weir.co.uk> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, July 15, 2003 6:39 PM Subject: Re: should you seperate indexes from tables in seperate datafiles?

> It's hot here. I wish I was at the beach and I feel like a rant.
>
> "oracle actually accesses indexes and tables serially"
>
> Is it just me or is this blindingly obvious?
> You cannot access the table data until you have completed accessing the
> index data
> because the index data contains the location of the table data.
>
> During an indexed query on a single table the index will be accessed, then
> the table,
> then the index,then the table, then the index,then the table then the
> index,then the table.
> If the index and the table are on the same disk then a lot of time will be
> taken up by
> head seek movement.
> If they are on the different disks then the "index" heads can locate their
> data and stay
> there - and the "data" heads can locate their data and stay there.
> Less head movement, less wasted time.
>
> That is the argument for what it is worth. Real life is of course vastly
> more complex than
> this and we are swimming in very muddy waters, which is why there is so
> much
> argument on the subject (raid salesmen - spit).
>
> Thanks for the vent
>
> Garry Gillies
>
>
>
>
>
>
> <rgaffuri_at_cox.net>
> Sent by: ml-errors_at_fatcity.com
> 15/07/03 15:49
> Please respond to ORACLE-L
>
>
> To: Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com>
> cc:
> Subject: should you seperate indexes from tables in
seperate datafiles?
>
>
> 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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Received on Tue Jul 15 2003 - 10:07:54 CDT