My personal story regarding the wait stuff (the Wait Interface as I usually call it) dates back to my days in Oracle many moons ago. On a big, internal list there, Kyle Hailey (who now works for Quest) talked about this new way of finding bottlenecks. Next, I stumbled upon Anjo's YAPP paper and that was it. I nearly fell off the ferry I was on while reading it. Since then, it has never ceased to surprise me that people are still reading and beleiving the books (like the ultimate books from the ultimate people, and all the others) where ratio after ratio after ratio is discussed. Where pure guesswork and magic are described as being scientific. Yuk.
Cary Millsap, I think, first coined the phrase "Checklist tuning". That's exactly what most tuners, DBA's and other nice people are wasting their time doing, instead of following the simple rules of looking at where the time goes. Without knowing where the time goes, how can anyone conclude anything?
But man, it gives us lots of work as long as people are reading those books. Perhaps the OakTable should write a book full of bad advise (why shouldn't we if anybody else can get away with it) and then lean back and wait for readers to call us :-))).
Mogens
Connor McDonald wrote:
I think you may have missed my sarcasm - I've been on
the anti-cache hit ratio bandwagon for a long time...
Cheers
Connor
--- DENNIS WILLIAMS <[EMAIL PROTECTED]> wrote:Connor - Cary Millsap presented the results of 10
trace files in a Hotsos
seminar I attended. The ratio ranged from a high of
108.57 down to a low of
0.79. The point is that the ratio is nowhere near
the oft-quoted 10,000.
This means that logical I/Os are not insignificant.
Even if physical I/O
were eliminated (all blocks cached, 100% cache hit
ratio), response time
would not drop to zero. This is why the emphasis in
tuning is shifting from
simple ratios to examining wait times. If the most
significant wait time is
physical I/O, then changing that will improve
overall performance. But if
the most significant wait time lies in another area,
then you may make
significant improvements in physical I/O and still
not improve overall
performance. I certainly wouldn't claim to be an
Oracle tuning expert, but I
believe that the new ideas on tuning that are
emerging provide a significant
step forw ard in making Oracle tuning more of a
logical process than a
collection of rules of thumb.
Dennis Williams
DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----Original Message-----
Sent: Wednesday, March 20, 2002 3:49 AM
To: Multiple recipients of list ORACLE-L
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 appeaseaman'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'mprimed to buy it
already.
I just recalled a legend, maybe. "Disk is 10,000
times slower than memory,
so memory access times are infinitesimal comparedtodisk access". Cary
Millsap covers this in his Hotsos Clinic. He hasruntests that prove "ain't
so". The point is that you can't just use ratiostotune 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 appeaseaman'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 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 canappeasea 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 MUSThavethe control file for
thedatabase from BEFORE the resetlogs operation,=== 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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