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March 2013

Enkitec’s Exadata Smart Flash Cache Hacking Session by Tanel Poder! (free stuff!!!)

We recently received our 3rd Exadata machine into Enkitec’s exalab. Now we have a V2, X2 and X3 there, in addition to ODA, Big Data Appliance (which comes with a beer-holder built in!) and an Exalytics box! So you understand why Karl Arao is so excited about it :-)

This occasion demands that we hack the hell out of all this kit soon! So, let’s have another (super-secret) hacking session!

This time, let’s see how the Exadata Smart Flash Cache works! (both for reads and writes). Note that we won’t cover Smart Flash Logging in this session (otherwise we’ll end up spending half a day on it :)

Parallel unfriendly

Take a look at the following Parallel section of a SQL Monitor report:

Any query which produces such a report won't care about how much parallel you're running because virtually all the time is spent by the query coordinator (which is a serial process) being busy.

In this case the query in question is quite simple:



select /*+ parallel(t,8) */ median(basket_amount) from whs.fact_sale t

The reason it behaves the way it does has everything to do with how Oracle executes it:

Execution Plan
----------------------------------------------------------
Plan hash value: 712547042

-----------------------------------------------------------------------------------------------------------------------------------------

Complete SAP projects in half the time : webinar

March 20, 2013, Wednesday, 10:00 am-11:30 am PST

Speaker:   Rick Caccia, Vice President Strategy at Delphix

To Register:  Click Here

Delphix accelerates SAP project delivery by eliminating redundant infrastructure and slow processes.

Delivering application projects quickly can immediately impacts revenues and earnings.  Most IT organizations can only fund a small number of projects in a given year which limits the ability of businesses to capture these market opportunities and operational efficiencies.

"Cost-free" joins - 2

In the previous post I've demonstrated an unexpected Nested Loop Join caused by an extreme data distribution. Although unexpected at first sight, the performance of the execution plan selected by the optimizer is decent - provided the estimates are in the right ballpark.Here is another case of an unexpected execution plan, this time about Merge Joins.

Merge Joins

In order to appreciate why the execution plan encountered is unexpected, first a quick summary about how Merge Joins work:A Merge Join is essentially a Nested Loop operation from one sorted row source into another sorted row source.

Texas BBQ Fun with Friends after Hotsos Symposium 2013

With some friends from the Netherlands and Estonia at the Hard Eight BBQ at 688 Freeport Parkway in Coppell, Texas (+1) for food and another (+1) for the Texas experience. What a fun way to decompress after a brain stuffing week at Hotsos!

In the queue by the BBQ pit.

In the queue by the BBQ pit.

Register to IOUG COLLABORATE 13 and Get an Hour of My Time

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Spring is a very active conference season for me. I might be going to half a dozen conferences in 3-4 months. That’s a lot of travel, but I look forward to all of them. The conference I’m probably looking forward to the most this year is IOUG COLLABORATE. It might be because:

Webinar - Back to the Future: Oracle SQL Performance Firefighting using AWR

It's webinar time again! On March 26, Embarcadero will once again provide sponsorship for my webinar entitled "Back to the Future: Mining AWR Data for Oracle SQL Performance".

Abstract

Total Cost of Ownership (TCO) : The clue is in the name!

When you read the term “Total Cost of Ownership” (TCO), the word “Total” is pretty important!

Here is a paraphrased conversation I had recently…

  • Person: Product X is free!
  • Myself and others: The staff training costs to enable the long term support of product X, are not free though. Added to that, these people still have to support products Y and Z, so you are adding to their workload. You might even have to add people to the existing team, so the TCO may be far from free.
  • Person: But the product is free!

You can see where this is going. :)

Not all Deadlocks are created the same

I've blogged about deadlocks in Oracle at least once before. I said then that although the following message in deadlock trace files is usually true, it isn't always.

The following deadlock is not an Oracle error. Deadlocks of  
this type can be expected if certain SQL statements are      
issued. The following information may aid in determining the 
cause of the deadlock.

So when I came across another example recently, it seemed worth a quick blog post. Not least for the benefit of other souls who hit the same issue (and probably hit Google moments later).

But while it's easy to say - "Hey! Look! I found an exception! Aren't I clever?" - it occurred to me that actually Oracle's capabilities in this area might be underrated by raising the occasional anomaly. Because the truth is