Bjørn Engsig wrote:
Cary Milsap from hotsos has much data to confirm an approximate 1:100 ratio
between LIO time and PIO time.
Can we therefore conclude, that the buffer cache hit ratio should be 99%? :-)
Rgds, Bjørn.
On Wednesday 20 March 2002 10:48, Connor McDonald wrote:Some rudimentary testing on a laptop here (500Mhz,
512M RAM, typical single disk)
a) visiting a single block via 4,000,000 logical IO's
got me approx 35000 gets/sec
b) repeated full table scans similar system got me
approx 350 phys reads/sec
After this extensive, thorough and exhaustive
exercise, I can definitely say that memory access
versus disk access (as it pertains to Oracle) is 100
times faster on this machine in single user mode
I think we can generalise this to be the rule for all
servers under all conditions :-)
Connor
--- "Freeman, Robert " <[EMAIL PROTECTED]>
wrote: > I've heard the disk vs. memory arguments
before, butnever have seen
quantifiable data either way... if anyone has any,
I'd love to see it.
RF
Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration
The Cigarette Smoking Man: Anyone who can appease a
man's conscience can
take his freedom away from him.
-----Original Message-----
Sent: Monday, March 18, 2002 5:54 PM
To: Multiple recipients of list ORACLE-L
Robert - So THAT is the title of your next book. I'm
primed to buy it
already.
I just recalled a legend, maybe. "Disk is 10,000
times slower than memory,
so memory access times are infinitesimal compared to
disk access". Cary
Millsap covers this in his Hotsos Clinic. He has run
tests that prove "ain't
so". The point is that you can't just use ratios to
tune Oracle, but need to
look at wait times.
Dennis Williams
DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----Original Message-----
Sent: Monday, March 18, 2002 1:04 PM
To: Multiple recipients of list ORACLE-L
So, does the CoO (Church of Oracle) have an
infallibility doctrine then???
... From the Book of Oracle, chapter 5 ...
...and the DBA did look upon his database, and he
saw it was good.
His tablespace datafiles being distributed tither
and fro, spread amongst
the
platters of his disks. And he did complete that
which was called
documentation,
and then he rested from his labors, and drank
Mountain Dew Code Red...
:-)
Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration
The Cigarette Smoking Man: Anyone who can appease a
man's conscience can
take his freedom away from him.
-----Original Message-----
Sent: Monday, March 18, 2002 12:25 PM< br>To: Multiple recipients of list ORACLE-L
Hey, you're an author!
I expect perfection, grace and infallibility. ;)
Jared
On Monday 18 March 2002 07:33, Freeman, Robert
wrote:And hey, it was Sunday morning at 0700something... what do youexpect from me anyways??? :-)))))))
RF
Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration
The Cigarette Smoking Man: Anyone who can appeasea man's conscience cantake his freedom away from him.
-----Original Message-----
Sent: Sunday, March 17, 2002 6:43 PM
To: Multiple recipients of list ORACLE-L
On Sunday 17 March 2002 07:53, Freeman, Robertwrote:1. You do not open the database to users untilAFTER you do a backup
(hotor cold, dosen't mater) at point t2.Well, yeah, that was the point. It doesn't haveto be a cold backup, butsince you can't do any work, it may as well be acold backup.Jared2. There is a method of recovering a database(8i +) after RESETLOGS hasbeen
issued with archived redo logs. I discussed itin my DBA World Tourbackup and
recovery presentation. To do this, you MUST havethe control file for
thedatabase from BEFORE the resetlogs operation,and backup of the controlfile from AFTER the same operation. I've donethis about 3 times intestingand it works fine but it very very picky aboutthe control file images.RF
Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration
The Cigarette Smoking Man: Anyone who canappease a man's conscience cantake his freedom away from him.
-----Original Message-----
Sent: Friday, March 15, 2002 7:28 PM
To: Multiple recipients of list ORACLE-L
Hi Jared,* You *have* to take a COLD backup of thedatabase after usingresetlogs.(Not required - a Hot backup and archivelogs is adequate. All hotbackups /archive logs prior to that are invalid,though...)Consider the following:
Time:
t0: database restored
t1: database opened with RESETLOGS
t2: hot backup started ( database in archivelog mode )t3: users input very important transactions
t4: database crashes, and must be restored
How will you recover the transactions fromtime t3?As long as the online redologs are available,this should be no problem.I have successfully recovered databases where alog switch did not occurand recovery had to use an online redo log. (Iam assuming that the lostdatafiles will be restored from this hot backupfresh off the tapes)On the other hand, if the online redolog ishosed you have lost thetransactions anyway, _regardless_ of the factthat a Cold backup was=== message truncated ===
=====
Connor McDonald
http://www.oracledba.co.uk (mirrored at
http://www.oradba.freeserve.co.uk)
"Some days you're the pigeon, some days you're the statue"
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