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Home -> Community -> Usenet -> c.d.o.server -> Re: URGENT! Writes to Disk while Doing a SELECT statement?
Satar
You may be seeing the effects of delayed block cleanout, where your SELECT statement is the first statement to hit blocks that have been updated but not written out yet.
Also, run an explain plan to check there are no sort operations taking place. There are other operations than just an order by that will cause sorts.
It is possible that after the first run (or even for the first run if someone else has hit the same blocks) that the blocks you're after are in memory, hence no disk reads.
HTH. Pete
Satar wrote:
> Please Help...
> Situation:
> Test Server running Oracle 7.3.4.0.1 on Solaris 2.6 release 5/98.
> I'm the only one logged in on the server and database.
> Sun E450 Server attatched to a A5000. (software Raid 0+1).
>
> I'm observing the I/O of the Sun E450 Server. I do a Basic select on a view
> (which is join of 5 tables). It is a basic select with no sorting (no Order
> by). I notice that three of my datafiles are being written to: rbs, temp, and
> my data datafile.
>
> My question:
> What is going on? What is Oracle doing? Why did I see write activity (every
> time) and no Read activity (Maybe there was Read activity only the first time
> running the SELECT statement?).
>
> Bonus Question: I'm experiencing a 50% performance loss with the same
> database on two servers. The only thing I can think of (which isn't logical)
> is that the high performance database is on Solaris 2.5.1 and the low
> performance database is on 2.6. Can anyone relate to this?
>
> The High(er) performance database is running on a single 176Mhz processor Sun
> Ultra 2 attached to an Andataco (running RAID 5) while the low performance
> database is running on quad 400mhz processor Sun E450 attached to a Sun A5000
> (Running RAID 0+1). The Database (consisting of 500MB...Yes, I mean Megabytes)
> is configuired the same (memory, tables, indexes, init<sid>.ora and all). I
> looked into Hardware, Network, RAID setup, ect. and came up blank. The only
> thing that I didn't check into, is the OS. So, should I consider the OS as a
> performance factor?
>
> Not in my 2.5 years have I heard/seen such a thing on Solaris. Thanks in
> advance, to those of you who reply to this post.
>
> Regards,
> Satar
> Oracle DBA/UNIX System Admin
> "Opinions are the result of the voices in my head only,
> and do not reflect my employer or Oracle Corporation."
>
> PS Thomas Kyte, if I ever needed you (these past 2 years)...The time is now.
>
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Regards
Pete
Peter Sharman Email: psharman_at_us.oracle.com WISE Course Development Manager Phone: +1.650.607.0109 (int'l) Worldwide Internal Services Education (650)607 0109 (local)San Francisco
"Controlling application developers is like herding cats."
Kevin Loney, ORACLE DBA Handbook
"Oh no it's not! It's much harder than that!"
Bruce Pihlamae, long term ORACLE DBA
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