Are you getting the most out of your Exadata performance? Part 1

August 8, 2011 By 4 Comments

In almost all of the Exadata migration projects I’ve been part of, the client sees immediate speedup & performance increase when testing their workload on Exadata (of course, we’ve made sure that we do plan & execute the tasks right). However, my performance geek’s nature usually doesn’t allow to stop there and leave the client with just 2x or 3x performance increase. For data warehousing and reporting workloads, Exadata can do much better than just 2-3x performance increase! 

This is why I will write this article series about Getting the Most out of your Exadata Performance. I will write a bunch of random articles, based on my experience and lessons learned – and some day I may consolidate it all into a more formal paper.

So, here’s the first article (PDF format).

Enjoy! :-)

(Leave your comments & feedback here …)

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Secret hacking session – full scans, direct path reads, object level checkpoints, ORA-8103s!

August 6, 2011 By 11 Comments
FREE STUFF !!! FREE STUFF !!! FREE STUFF !!!
At the last week’s Expert Oracle Exadata virtual conference both me and Kerry touched the topic of how smart scan (and direct path read) decisions are done for each scanned segment during the SQL execution runtime – and not by the optimizer during the optimization phase.
I got a few follow-up questions about this yesterday and I also recall a similar question after my Understanding Exadata Performance Metrics presentation I did for UKOUG in London in April.
I think this is a topic which deserves some deeper coverage and so I decided I’ll do another secret hacking session on Tuesday 9th August (2011) 9-11am PDT.
The topics (hopefully) covered will be:
  1. How do full table scans work
  2. How and why do the “ORA-8103: object no longer exists” happen
  3. How does Oracle (11g) decide between a buffered full table scan and a direct path read scan (plus smart scan in Exadata)
  4. What’s the difference between an object_id and data_object_id?
  5. and more!
Note that while I do touch the Exadata topic a bit too, this session is generic and useful for anyone full scanning tables on any Oracle database… :)
This event is free and you can sign up here:

P.S. I will record the event and publish the video too. So if you’re in Australia or Hong Kong, no need to stay up late ;-)

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Training Schedule for 2011 and Public Appearances

July 28, 2011 By Leave a Comment
Online Seminars
A lot of people have asked me about whether I’d be doing any more seminars in the future. And the answer is yes – at least this year (might be too busy running a company the next year ;-)

I have finally put together the schedule for my 2011 seminars. In addition to the Advanced Oracle Troubleshooting seminar I will also deliver my Advanced Oracle SQL Tuning and Oracle Partitioning and Parallel Execution for Performance seminars, which I have done only onsite in past.

So, check out the seminars page:
Also don’t forget the Expert Oracle Exadata virtual conference next week!

Public Appearances

Oracle OpenWorld 2. October
  • I will talk about Large-Scale Consolidation onto Oracle Exadata: Planning, Execution, and Validation
  • Session ID 09355

Maybe I’ll lurk around the UKOUG venue as well in december ;-)

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Expert Oracle Exadata virtual conference

July 22, 2011 By 4 Comments

Today is the last day for getting the early bird’s rate!

http://blog.tanelpoder.com/seminar/expert-oracle-exadata-virtual-conference/

Also, our book will be out on Monday!

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Enabling and Reading event 10046 / SQL Trace

July 20, 2011 By 1 Comment

As I’m done with the book and back from a quick vacation (to Prague, which is an awesome place – well, at least during the summer) I promised (in Twitter) that now I’d start regularly writing blog articles again. In a separate tweet I asked what to write about. Among other requests (which I’ll write about later), one of the requests was to write something about enabling and reading SQL trace files… 

I am probably not going to write (much) about SQL trace for a single reason – Cary Millsap has already written a paper so good about this topic, that there’s no point for me to try to repeat it (and my paper wouldn’t probably be as clear as Cary’s).

So, if you want to get the most out of SQL Trace, read Cary’s Mastering Performance with Extended SQL Trace paper:

 

The above link directs you to Method-R’s article index, as there’s a lot of other useful stuff to read there.

Wow, now I’m done with my first request – to write something about SQL Trace :-)

 

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RAC hack!

July 6, 2011 By

In other words – FREE STUFF!!!

Riyaj Shamsudeen does a free RAC hacking session on 12 July!

He will demonstrate how the LMS background process works, with the help of OS tracing tools like truss and DTrace.

Sign up here!

 

Update:

A video recording of the session can be found here: http://www.vimeo.com/26798681

 

 

Filed Under: Oracle Tagged With: ,

What is the purpose of segment level checkpoint before DROP/TRUNCATE of a table?

July 6, 2011 By 27 Comments
There was a very good question asked in Oracle-L list today, which has bothered me too in past.
The question was:
What is the purpose of a segment level checkpoint before DROP/TRUNCATE of a table?
 
In other words, why do we have to wait for the enq: RO – fast object reuse wait event (and in 11.2 the enq: CR – block range reuse ckpt wait) when dropping & truncating segments?
 
I’m not fully confident that I know all the real reasons behind this, but it could be related to the need to get rid of segment’s dirty buffers in buffer cache, before dropping the object.
 
Imagine this:
 
  • You have a large buffer cache and you drop table A without checkpointing the dirty buffers.  
  • Immediately after the drop succeeds (some buffers are still dirty in cache) some other segment (table B) reuses that space for itself and writes stuff into it.
  • A few seconds later, DBWR wakes up to find & write some dirty buffers to disk (anything it finds from its lists). As there are some old & dirty blocks of table A still in the cache, they get written to disk too, overwriting some of the new table B blocks!

  

So, this is one reason why you should checkpoint the blocks to disk before dropping (or truncating) a segment. Of course you might ask that why doesn’t DBWR just check whether the dirty buffer is part of an existing object or a dropped one when it walks through its dirty list? It could just discard the dirty buffers of dropped objects it finds. It would be doable – but I also think it would get quite complex. DBWR is a low level background proces, understanding the cache layer and dealing with physical datablocks in a file# = X block offset = Y. It doesn’t really know anything about the segments/objects which use these blocks. If it should start checking for logical existence of an object, it would have to start running code to access (a much higher level concept) data dictionary cache – and possibly query data dictionary tables via recursive calls, etc, so making it much more complicated.
 
So, this logic may just be matter of implementation, it’d be too complex to implement such selective discarding of dirty buffers, based on a higher-level concept of existence of a segment or object. Dropping and truncating tables so frequently, that these waits become a serious problem (consuming significant % of response time) indicate a design problem anyway. For example, former SQL server developers creating multiple temporary tables in Oracle – for breaking a complex query down into smaller parts, just like they had been doing it in SQL Server.
 
Anyway, here’s what I think about this – I’d love to hear other opinions, if you think otherwise!
Filed Under: Oracle Tagged With:

The First Exadata Virtual Conference in the World!

July 4, 2011 By 6 Comments

We have been secretly planning something with Kerry Osborne – and now it’s official – we will host The First Exadata Virtual Conference in the World, on 3-4 August 2011.

This conference takes place a couple of weeks after our Expert Oracle Exadata book is published (on 18. July – check out the awesome new cover design). So, we thought it’d be a good idea to run this conference, where we can explain some things in a different format, do live demos and answer questions that attendees have.

On the first day Kerry and Randy will talk about some serious fundamentals of Exadata, like how Exadata Smart Scan Offloading works and how to make the IO resource manager work for you (especially important in mixed workload consolidated environments).

And on the second day we’ll dig even deeper, with Andy Colvin talking about how to survive Exadata patching (he has patched more Exadatas than anyone else I know) and me following up with some complex performance troubleshooting stories I’ve encountered recently (trust me – there’s a LOT of issues to troubleshoot ;-)

About the Conference:

Since its release, Oracle Exadata quickly became a hit. Due to the relative “youth” of Exadata technology and internal behavior changes introduced with frequent patch-sets, there’s not much up-to-date quality technical information and know-how available to public. This virtual conference brings you a chance to learn from the leading Exadata experts, from their experience of working with real Exadata environments, from Exadata V1 to the latest X2-8. Additionally, there is plenty of Q&A time scheduled, so you can also get answers to your Exadata-related questions.

The speakers are probably some of the most experienced Exadata consultants in the world, in the field of Exadata deployment, migration, performance, and troubleshooting. Also, Kerry, Randy and Tanel are the authors of the Expert Oracle Exadata book published by Apress in July 2011.

Dates:

  • 3-4 August 2011

Location:

  • Online (or should I say “the Cloud” ;-)

Duration:

  • 8am – 12pm (PST) on both days – 2 x 1.5h sessions on each day, with Q&A sessions and a break in between

Speakers:

  • Kerry Osborne, Randy Johnson, Andy Colvin from Enkitec
  • Tanel Poder from right here :-)

All of the speakers are hard-core hands-on professionals, having worked on many different real-life (production) Exadata environments of their clients. Enkitec dudes didn’t stop there, they bought a half rack for themselves, just for playing around with it. Yeah (+1 from me), some people buy a red hot Ferrari, some buy a red hot computer rack with an X on it :-)

Price:

  • 375 USD (early bird until 22. July), 475 regular price

More information, abstracts and registration:

I don’t think you’ll find an Exadata learning opportunity like this from anywhere else (and any time soon), especially considering the price!

This conference is so hot, that one of the attendees managed to sign up to it even before I had published this page to the world! :-)


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Another cache buffers chains latch contention troubleshooting example using LatchProf

June 30, 2011 By Leave a Comment

One of my blog readers recently dropped me an email noting that he had noticed some cache buffers chains latch contention recently and successfully troubleshooted it with LatchProf. I asked if he’d like to blog about it and here’s the article:

 

Cache buffer chains latch contention typically shows up when some execution plans go bad, switching to nested loops or filter loops and revisiting the same table (or index) blocks very frequently…

 

Filed Under: Oracle Tagged With: ,

Advanced RAC Training by Oracle RAC expert Riyaj Shamsudeen

June 30, 2011 By 7 Comments

If you’ve troubleshooted (or tuned) RAC then you probably already know Riyaj Shamsudeen and his Orainternals blog & website (links below).

Anyway, since I started delivering my Advanced Oracle Troubleshooting classes some years ago, many people asked whether I would do a similar class for RAC. I had deliberately left out the RAC-specific stuff from my troubleshooting material, because it’s a very wide and complex topic and I feel like before trying to master RAC troubleshooting, you should master troubleshooting of regular single instance databases anyway. I realized that I didn’t have the time to build (and maintain) yet another set of trainig material, especially on so complex topic as RAC performance & troubleshooting. 

So, having seen Riyaj’s impressive work and his presentations at various conferences, I asked whether he would be interested in building a RAC troubleshooting class, going from fundamentals to advanced topics – and he said yes. By now we are that far that I’m happy to announce the first Advanced RAC online seminars by Riyaj Shamsudeen (split across two weeks of online sessions, 4-hours per day, in end of august and september).

We initially called the seminar “Advanced RAC Troubleshooting” but then realized, that there are some closely related non-troubleshooting topics to be covered, like fundamental concepts, internals and also how to configure RAC for performance (so that you wouldn’t have to troubleshoot performance later :-)

We’ll use the same infrastructure and seminar philosophy as I do in my own online seminars, it’s just that this is Riyaj’s material and he will deliver it too.

You can read more about the seminar content, dates and sign up at the seminars page:

Seminars:

Riyaj’s blog:

Riyaj’s website (articles, slides etc):

 

Let the RAC hacking begin! ;-)

 

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