Tanel Poder's blog: IT & Mobile for Geeks and Pros
Oracle, Exadata, Performance, Troubleshooting - Mobile Life and Productivity.
So, what do you think is the most fundamental difference between NESTED LOOPS and HASH JOINS?
This is not a trick question. You’re welcome to write your opinion in the comments section – and I’ll follow up with an article about it (my opinion) later today…
Update: The answer article is here:
I’ve been tracking my business travel with Tripit.com‘s awesome service for about 2 years now.
After getting back from my Tallinn->Helsinki->New York->Detroit->New York->San Francisco->New York->Helsinki->Tallinn trip yesterday, Tripit reported that I have flown 1 007 509 km during my business trips (American readers, that’s about 42 miles ;)
Check yourself below :)
Tripit says I’ve visited 71 different cities in 27 countries within the last two years.
Here’s the map of places where I’ve visited my clients, done training or spoken at conferences:
Actually there’s probably couple of more cities where I’ve been in the last two years, for some reason Tripit doesn’t recognize my trip to Melbourne (but it does show the visit to Sydney which I did during the same trip).
Anyway, the conclusion here is that I think I’ve done enough flying for now. Now I plan to stay at home for a loooong time (I mean at least 3-4, maybe even 5 weeks in a row!!! ;)
But seriously, what I’ve decided is that:
Ok, enough of self-promotion and advertising, back to work ;-)
P.S. I will publish my online seminar schedule “very soon now”!!!
P.P.S. I’m not affiliated with Tripit.com by any means business-wise, but if you travel frequently, then I recommend you to check out their awesome service (and iPhone app). The basic version is free, but I just decided to upgrade to Pro after couple of years of using it!
Thanks to everybody who attended my OCW hacking session!
Sorry to guys who attended via webinar – I’ll do the session again in a few weeks, with audio from end to end hopefully! And I will get someone to assist me with monitoring the transmission quality and attendee questions etc.
Note that this stuff is mostly for hacking and fun – don’t use the undocumented stuff in production!
The links are below:
Download scripts & Tools:
Rlwrap links:
Diagnostic events:
X$TRACE
I haven’t written any articles on X$TRACE yet, but you can find some stuff from one of my very old presentations:
Or just type:
ALTER TRACING ENABLE “10704:4:ALL”
Where 10704 is the KST event number, 4 is the level and ALL means all Oracle PIDs (Oracle PIDs, not OSPID’s).
After hours of careful planning (as you’ll see from the images) I decided to webcast my tomorrow’s Oracle Closed World hacking session…
This session isn’t necessarily going to be useful, but it definitely should be fun !!!
You can register here:
So, which number takes more bytes inside an Oracle row?
A: 123
B: 1000000000000000000000000000000000000
And the correct answer is … (drumroll) … A! The “big” number 1000000000000000000000000000000000000 actually takes less space than the “small” 123!
Let’s verify this:
SQL> select vsize(123) A, vsize(1000000000000000000000000000000000000) B from dual;
A B
---------- ----------
3 2
WTF? Why does such a small number 123 take more space than 1000000000000000000000000000000000000 ?
Well, the answer lies in how Oracle stores numbers. Oracle NUMBER datatype doesn’t store numbers in their platform-native integer format. Oracle uses it’s own format which stores numbers in scientific notation, in exponent-mantissa form. More details about this here.
You can use the DUMP sql function to see the actual binary value of the number data stored:
select dump(123) from dual; DUMP(123) --------------------- Typ=2 Len=3: 194,2,24 SQL> select dump(1000000000000000000000000000000000000) from dual; DUMP(10000000000000 ------------------- Typ=2 Len=2: Typ=2 Len=2: 211,2
So, although the number 1000000000000000000000000000000000000 is bigger than 123, when stored in base-10 exponent form, it really carries much less information in it than 123 (1 x 10^36 vs 123 x 10^0). Oracle doesn’t need many bits for keeping the precision of this large value as it happens to be a power of 10.
See what happens when I store a number only slightly bigger or smaller than the original large number, now the stored number requires much more storage for keeping the required precision:
SQL> select dump(1000000000000000000000000000000000000+1) from dual; DUMP(1000000000000000000000000000000000000+1) ------------------------------------------------------- Typ=2 Len=20: 211,2,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2 SQL> select dump(1000000000000000000000000000000000000-1) from dual; DUMP(1000000000000000000000000000000000000-1) ----------------------------------------------------------------------------------------- Typ=2 Len=19: 210,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100
Here’s the list of events where I’ll speak this year:
Michigan OakTable Symposium 2010
Ann Arbor, MI
16-17 September 2010
Considering the concentration of OakTable members there, this will be an awesome event!
I will be delivering my “Back to Basics: Choosing The Entry Point to Performance Troubleshooting Wisely” and “Understanding LGWR, log file sync waits and commit performance” sessions there.
Promo video:
http://www.oaktable.net/media/michigan-oaktable-symposium-2010-promo
Agenda & Registration:
http://michigan.oaktable.net/
Oracle Open Closed World
San Francisco, CA
19-22. September
Note that I won’t be speaking at the official Oracle Open World conference, but I will be speaking at a secret underground event there, about some really fun stuff, like deep internals, hacking, kernel tracing and of course advanced troubleshooting ;-) And rest of the time I’ll be in some bar.
NYOUG Fall 2010 Training Session
Manhattan, NYC, NY
16 November 2010
This is a full day seminar organized by NYOUG. I will be delivering my “Scripts and Tools for Oracle Troubleshooting and Advanced Performance Analysis” session there. It’s an updated version of the material I delivered at the Hotsos Symposium Training Day this year.
Agenda & Registration:
http://www.nyoug.org/upcoming_events.htm#NYOUG_Training_Days
UKOUG Tech & EBS Conference (to be confirmed)
Birmingham, UK
29 November – 1 December 2010
I submitted four papers to UKOUG Tech&EBS conference, so if all goes well, I’ll be there in end of Nov/beginning of Dec too.
