Re: Fav. Urban Legend...Mem vs Disk

I always thought 42 was a good number. Perhaps I was wrong.

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 " <Robert_Freeman_at_csx.com>
>>wrote: > I've heard the disk vs. memory arguments
>>before, but
>>
>>>never 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.
>>>dwilliams_at_lifetouch.com
>>>
>>>
>>>-----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
>>>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 0700
>>>>
>>>something... what do you
>>>
>>>>expect from me anyways??? :-)))))))
>>>>
>>>>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: Sunday, March 17, 2002 6:43 PM
>>>>To: Multiple recipients of list ORACLE-L
>>>>
>>>>On Sunday 17 March 2002 07:53, Freeman, Robert
>>>>
>>>wrote:
>>>
>>>>>1. You do not open the database to users until
>>>>>
>>>AFTER you do a backup
>>>(hot
>>>
>>>>>or cold, dosen't mater) at point t2.
>>>>>
>>>>Well, yeah, that was the point. It doesn't have
>>>>
>>>to be a cold backup, but
>>>
>>>>since you can't do any work, it may as well be a
>>>>
>>>cold backup.
>>>
>>>>Jared
>>>>
>>>>>2. There is a method of recovering a database
>>>>>
>>>(8i +) after RESETLOGS has
>>>
>>>>>been
>>>>>issued with archived redo logs. I discussed it
>>>>>
>>>in my DBA World Tour
>>>
>>>>>backup and
>>>>>recovery presentation. To do this, you MUST have
>>>>>
>>>the control file for
>>>the
>>>
>>>>>database from BEFORE the resetlogs operation,
>>>>>
>>>and backup of the control
>>>
>>>>>file from AFTER the same operation. I've done
>>>>>
>>>this about 3 times in
>>>
>>>>testing
>>>>
>>>>>and it works fine but it very very picky about
>>>>>
>>>the control file images.
>>>
>>>>>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: Friday, March 15, 2002 7:28 PM
>>>>>To: Multiple recipients of list ORACLE-L
>>>>>
>>>>>
>>>>>Hi Jared,
>>>>>
>>>>>>>* You *have* to take a COLD backup of the
>>>>>>>
>>>database after using
>>>
>>>>>>resetlogs.
>>>>>>
>>>>>>>(Not required - a Hot backup and archive
>>>>>>>
>>>logs is adequate. All hot
>>>
>>>>>>backups /
>>>>>>
>>>>>>>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 archive
>>>>>>
>>>log mode )
>>>
>>>>>>t3: users input very important transactions
>>>>>>t4: database crashes, and must be restored
>>>>>>
>>>>>>How will you recover the transactions from
>>>>>>
>>>time t3?
>>>
>>>>>As long as the online redologs are available,
>>>>>
>>>this should be no problem.
>>>
>>>>>I have successfully recovered databases where a
>>>>>
>>>log switch did not occur
>>>
>>>>>and recovery had to use an online redo log. (I
>>>>>
>>>am assuming that the lost
>>>
>>>>>datafiles will be restored from this hot backup
>>>>>
>>>fresh off the tapes)
>>>
>>>>>On the other hand, if the online redolog is
>>>>>
>>>hosed you have lost the
>>>
>>>>>transactions anyway, _regardless_ of the fact
>>>>>
>>>that 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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>

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