Search

OakieTags

Who's online

There are currently 0 users and 33 guests online.

Recent comments

performance

The First Exadata Virtual Conference in the World!

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 #2970a6; text-decoration: none; padding: 0px; margin: 0px;\" href="http://blog.tanelpoder.com/wp-content/plugins/wordpress-feed-statistics/feed-statistics.php?url=aHR0cDovL3d3dy5hcHJlc3MuY29tLzk3ODE0MzAyMzM5MjM=">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! :-)


Another cache buffers chains latch contention troubleshooting example using LatchProf

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…

 

Advanced RAC Training by Oracle RAC expert Riyaj Shamsudeen

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! ;-)

 

IOUG Select Journal Editor’s Choice Award 2011

In May I received the IOUG Select Journal Editor’s Choice Award for my Systematic Oracle Latch Contention Troubleshooting article where I introduced my LatchProfX tool for advanced drilldown into complex latch contention problems (thanks IOUG and John Kanagaraj!).

As the relevant IOUG webpage hasn’t been updated yet, I thought to delay this announcement until the update was done – but I just found an official enough announcement (press release) by accident from Reuters site:

Woo-hoo! :-)

The article itself is here:

Thanks to IOUG crew, John Kanagaraj and everyone else who has read, used my stuff and given feedback! :-)

Give Me a Hint – How were These Autotrace Execution Statistics Achieved?

June 27, 2011 I recently received an email asking why different performance is achieved when a FIRST_ROWS hint, FIRST_ROWS(100) hint, and an unhinted version of the query are executed.  This seems to be a simple problem, yet it might also be an interesting problem.  I thought that it might be helpful to transform my response into a blog article (allowing the [...]

Video

Here’s a video of the presentation that I did as the keynote for the Turkish Oracle Users’ Group conference earlier on this year. Recording courtesy of the people at Formspider.

The topic is about tuning a two-table join, and the video is about an hour long (so there’s a lot more that could be  said on the topic, and one day I might do a half  day “masterclass” on it).

Optimisation

A question came up on Oracle-L recently about the difference in work done by the following two queries:

SELECT /*+ RULE */
	DOM_NAME
FROM
	DOMAINS,
	TABLE(CAST(:B1 AS DOMAIN_LIST)) DL
WHERE
	DOM_NAME = DL.COLUMN_VALUE
;

SELECT
	DOM_NAME
FROM
	DOMAINS
WHERE
	DOM_NAME IN (
		SELECT	COLUMN_VALUE
		FROM	TABLE(CAST(:B1 AS  DOMAIN_LIST))
	)
;

Before saying anything else, I should point out that these two queries are NOT logically equivalent unless you can guarantee that the table() operator returns a unique set of values – and Oracle doesn’t allow uniqueness to be enforced on collections.

However, the author of the question had ensured that the results from the table() operator contained no duplicates so the two versions of the query returned the same result set. The question is, why does one query do fewer buffer visits than the other – as evidenced by the results from sql_trace and tkprof.

Rule-based Join
===============

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.01       0.01          0          0          0           0
Fetch        1      0.86       0.86          0     200047          0      115195
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.87       0.87          0     200047          0      115195

Rows     Row Source Operation
-------  ---------------------------------------------------
 115195  NESTED LOOPS  (cr=200047 pr=0 pw=0 time=6355 us)
  99704   COLLECTION ITERATOR PICKLER FETCH (cr=0 pr=0 pw=0 time=284 us)
 115195   INDEX RANGE SCAN DOM_NAME_IDX (cr=200047 pr=0 pw=0 time=3191 us)(object id 54309)

CBO with subquery
=================

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.01       0.01          0          0          0           0
Fetch        1      0.78       0.78          0     157986          0      115195
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.80       0.80          0     157986          0      115195

Rows     Row Source Operation
-------  ---------------------------------------------------
 115195  NESTED LOOPS (cr=157986 pr=0 pw=0 time=4720 us cost=536 size=6141 card=267)
  99704   SORT UNIQUE (cr=0 pr=0 pw=0 time=417 us)
  99704    COLLECTION ITERATOR PICKLER FETCH (cr=0 pr=0 pw=0 time=259 us)
 115195   INDEX RANGE SCAN DOM_NAME_IDX (cr=157986 pr=0 pw=0 time=3353 us cost=2 size=21 card=1)(object id 54309)

Notice how the optimizer has unnested the subquery and introduced a “sort unique” – this demonstrates the optimizer’s recognition that the two queries are not logically identical. However, the number of rows from the collection is the same (99,704) and the number of rows after joining is the same (115,195) – the data sets have been rigged so that it is a fair comparison. So why does the explicit join take 200,047 buffer visits when the transformed  subquery approach take only 157,986 buffer visits.

The answer is that you can visit buffers without doing “logical I/Os” – and this benefit accrues most frequently to indexed access paths. Thanks to the way Oracle has sorted the collection before doing the join the nested loop follows the second index (dom_name_idx) in order – this increases the chance that index blocks that were used in the previous cycle of the loop will be re-used in the next cycle, which means that Oracle need not release the pins on the index blocks, but can revisit them incrementing the statitsic: “buffer is pinned count”.

I have to say that I haven’t proved that this is exactly what was happening, but when I suggested to the person who had asked the question that he re-run and check to see if the decrease in “session logical reads” was balanced by an increase in “buffer is pinned count” the answer seemed to confirm the hypothesis. [Correction (see comment #1 from Randolf): the results didn't confirm the hypothesis - but I think that' s because of the change in "pinning" that Randolf describes, so I'll have to find a way to confirm the hypothesis some other time.]

 

HOWTO: XML Partitioning and Multiple XMLIndex Structures

Although not a “pure” XML partitioning example, that is partitioning data on criteria within the XML document, and before I forget to mention this exercise, I would like to point out the following URL:

http://forums.oracle.com/forums/thread.jspa?threadID=2234618

This small exercise was setup based on questions / comments from a reader on this blog regarding the ”
Structured XMLIndex (Part 3) – Building Multiple XMLIndex Structures” content after heaving trouble to setup structured and unstructured local XMLIndexes.

The forum link demonstrates howto:

  • Register a XML Schema for use with Binary XML storage
  • Create a RANGE partitioned table with a XMLType column (Binary XML Securefile storage)
  • Create a Unstructured LOCAL Partitioned XMLIndex (UXI)
  • Create multiple Structured local partitioned XMLIndexes (SXI)
  • Create secondary indexes on the Content Tables created by the SXI structures
  • The effects of different queries and their explain plan output making use of the UXI, SXI and partitioning

HTH

Real-World Performance Videos on YouTube – OLTP

In addition, here are some OLTP demos that demonstrate how much performance and throughput can be wasted by poor design and suboptimal database programming.

OLTP Performance – The Trouble with Parsing

width="640" height="510" src="http://www.youtube.com/embed/1oddFEyUAjs?rel=0" frameborder="0" allowfullscreen>

OLTP Performance – Concurrent Mid-Tier Connections

width="640" height="510" src="http://www.youtube.com/embed/xNDnVOCdvQ0?rel=0" frameborder="0" allowfullscreen>

Real-World Performance Videos on YouTube – Data Warehousing

Here are some videos of a data warehouse demo that the Real-World Performance Group has been running for a while now and we thought it was time to put them on YouTube. Hope you find them informative.

Migrate a 1TB Data warehouse in 20 Minutes (Part 1)

width="640" height="510" src="http://www.youtube.com/embed/q8zwfC_pruQ?rel=0" frameborder="0" allowfullscreen>

Migrate a 1TB Data warehouse in 20 Minutes (Part 2)

width="640" height="510" src="http://www.youtube.com/embed/qC5MT6qiPWw?rel=0" frameborder="0" allowfullscreen>

Migrate a 1TB Data warehouse in 20 Minutes (Part 3)

width="640" height="510" src="http://www.youtube.com/embed/2jWq-VUeOGs?rel=0" frameborder="0" allowfullscreen>

Migrate a 1TB Data warehouse in 20 Minutes (Part 4)

width="640" height="510" src="http://www.youtube.com/embed/hMXsrxyeRro?rel=0" frameborder="0" allowfullscreen>