Monday Apr 08, 2013

How does AUTO_SAMPLE_SIZE work in Oracle Database 11g?

When it comes to gathering statistics, one of the most critical decisions you have to make is, what sample size should be used? A 100% sample will ensure accurate statistics but could take a really long time. Where as a 1% sample will finish quickly but could result in poor statistics.

The ESTIMATE_PERCENT parameter in the DBMS_STATS.GATHER_*_STATS procedures controls the sample size used when gathering statistics and it default values is AUTO_SAMPLE_SIZE.

In an earlier blog post, we talked about the new implementation of AUTO_SAMPLE_SIZE in Oracle Database 11g in terms of its improvements in the speed and accuracy of statistics gathering compared to the old AUTO_SAMPLE_SIZE.

In this post, we will take a closer look at the how the new AUTO_SAMPLE_SIZE algorithm works and how it affects the accuracy of the statistics being gathered.

[Read More]

Wednesday Mar 13, 2013

Oracle Open World 2013 Call For Papers!

Believe it or not, it's time once again to start thinking about Oracle OpenWorld! The Oracle OpenWorld 2013 call for papers opens March 13th. Oracle customers and partners are encouraged to submit proposals to present at this year's Oracle OpenWorld conference, which will be held September 22 - 26, 2013 at the Moscone Center in San Francisco. Details and submission guidelines are available on the Oracle OpenWorld Call for Papers web site. The deadline for submissions is April 12th 2012 at 11:59 pm PDT. We look forward to checking out your sessions on the Optimizer, SQL Plan Management, and statistics!

This also means you need to start thinking of new slogans for this years optimizer bumper sticker! Details on how to submit an entry will follow shortly.

[Read More]

Monday Feb 11, 2013

How do adaptive cursor sharing and SQL Plan Management interact?

We've received a lot of questions about how adaptive cursor sharing (ACS) and SQL plan management (SPM) interact.  We discussed this briefly in one of the original SPM posts, but in this post, we'll explain the concepts of how the two features interact, and show an example. 

The simplest way to reason about the interaction is to remember that they are responsible for two different tasks.  ACS controls whether or not a child cursor is shared on a particular execution.  For each execution of the query, ACS considers the current bind values and decides if an existing child cursor can be shared or if the optimizer should be given the chance to find a better plan for the current bind values.  SPM controls which plans the optimizer may choose.  If a child cursor is bind-aware, the decision to share or not is made irrespective of whether the query is controlled by SPM.  But once the query and its current bind values are sent to the optimizer for optimization, SPM constrains the optimizer's choice of plans, without regard to whether this query is being optimized due to ACS.

[Read More]

Tuesday Feb 05, 2013

Upcoming events : RMOUG 2013

I'm really looking forward to the  Rocky Mountain Oracle User Groups Training days next week, at the Colorado Convention Center, as it will bring several new challenges for me.  I am going to be involved in three very different sessions at this years conference:

[Read More]

Wednesday Jan 09, 2013

How does SQL Plan Management match SQL statements to SQL plan baselines?

Happy New Year to all of our readers!

As more and more of your systems migrate to Oracle Database 11g, SQL Plan Management (SPM) is becoming increasingly popular as a mechanism to maintain plan stability and subsequently system performance. However, one of the key frustrations folks encounter when using SPM is that the SQL plan baseline they painstakingly created is not used.

[Read More]

Wednesday Nov 21, 2012

How do I create statistics to make ‘small’ objects appear ‘large’ to the Optmizer?

I recently spoke with a customer who has a development environment that is a tiny fraction of the size of their production environment. His team has been tasked with identifying problem SQL statements in this development environment before new code is released into production.

The problem is the objects in the development environment are so small, the execution plans selected in the development environment rarely reflects what actually happens in production.

[Read More]

Thursday Oct 04, 2012

Day 5 of Oracle OpenWorld 2012 October 4th

Its the last day of Oracle OpenWorld and we have saved the very best for last. So hopefully you are still awake and functioning at this stage!

Today, we present An Insider’s View of How the Optimizer Works (Session CON8457) at Moscone South - room 104. This session explains how the latest version of the optimizer works and the best ways you can influence its decisions to ensure you get optimal execution every time

We really hope you have enjoy the conference so far and will stop by our session this afternoon before you head off home!

Wednesday Oct 03, 2012

Day 4 of Oracle OpenWorld 2012 October 3rd

Thanks to all those who stopped by the demogrounds  to chat with the Optimizer developers and to check out what is new in the Oracle Optimizer over the last two days. Remember, today is the last day of the demogrounds, so if you haven't had a chance to stop by and collect you bumper sticker yet, do so today. The Optimizer developers will be there from 9:45 am until 4pm.

Don't forget our second technical session (Session CON8457) is tomorrow at 12:45pm.

Tuesday Oct 02, 2012

Day 3 of Oracle OpenWorld 2012 October 2nd

Hopefully you enjoyed yesterday, the first full day of technical sessions at Oracle OpenWorld and are ready for more today!

Today we give our first technical session, Oracle Optimizer: Harnessing the Power of Optimizer Hints (Session CON8455) at 1:15pm, in Moscone South - room 103. In this session we will discuss in detail how Optimizer hints are interpreted, when they should be used, why they appear to be ignored and what you can do if you have inherited a hint ridden application.

The Optimizer team will also be at the Oracle Database Demogrounds all day.  Demogrounds open at 9:45 am and run until 6pm. So stop by and find out what's new with the Optimizer and the statistics that feed it. Don't forget to pick up your Optimizer bumper sticker while you are there!

Monday Oct 01, 2012

Day 2 of Oracle OpenWorld 2012 October 1st

Oracle OpenWorld started yesterday and San Francisco is just buzzing with Oracle folks! If you are attending the conference don't miss the opportunity to chat with the Optimizer development team at one of our technical sessions or at the Oracle Demo grounds.

Our first technical session(Session CON8455) happens tomorrow at 1:15pm but the Oracle Optimizer Demo booth opens today. We are located in the database demo grounds, in Moscone South, booth number 3157.

Members of the Optimizer team will be available from 9:30am to 6pm today, to answer any Optimizer questions you might have and of course to dole out our limited edition Optimizer bumper stickers! The must have souvenir from this years conference

+Maria Colgan

Sunday Sep 30, 2012

Day 1 of Oracle OpenWorld 2012 September 30

Howard Street in San Francisco is closed. The large Oracle tent is up! Attendees are arriving by the plane load at SFO. It can only mean one thing ....

That's right!  Oracle OpenWorld officially starts today with the Oracle Users Forum. Ton's of great technical sessions selected by the Oracle User Groups get under way this morning at 8 am (Doh!). And of course, Larry's keynote is this evening 5:00 pm–7:00 pm, Moscone North. A must see, as he is bound to make some exciting announcements to get the show started!

Hope to see ya there!

Monday Sep 17, 2012

More on Oracle OpenWorld 2012

With only two weeks to go until Oracle OpenWorld, it is time to start planning your schedule. Every year folks ask me what Optimizer related sessions they should go and see at OpenWorld. Below are my top two picks for each day of the conference, to get your schedule started. .[Read More]

Wednesday Sep 05, 2012

Oracle OpenWorld 2012

I can't believe it's time for OpenWorld again!

Oracle OpenWorld is the largest gathering of Oracle customers, partners, developers, and technology enthusiasts. This year it will take place between September 30th and October 4th in San Francisco. Of course, the Optimizer development group will be there and you will have multiple opportunities to meet the team, in one of our technical sessions, or at the Oracle Database demogrounds.

[Read More]

Wednesday Aug 29, 2012

How do I restrict concurrent statistics gathering to a small set of tables from a single schema?

I got an interesting question from one of my colleagues in the performance team last week about how to restrict a concurrent statistics gather to a small subset of tables from one schema, rather than the entire schema. I thought I would share the solution we came up with because it was rather elegant, and took advantage of concurrent statistics gathering, incremental statistics, and the not so well known “obj_filter_list” parameter in DBMS_STATS.GATHER_SCHEMA_STATS procedure.

[Read More]

Friday Jul 13, 2012

Upcoming events: INOUG Oracle Training Day!

The Indiana Oracle User Group (INOUG) have been kind enough to ask me to present an all day Optimizer workshop at their annual training day on July 26th at Eli Lilly & Co. The workshop will consist of four 90 minute session and will explain the fundamentals of the cost based Optimizer and the statistics that feed it, as well as providing a methodology for diagnosing and resolving SQL execution performance problems.

The workshop begins with an in-depth look at statistics and statistics maintenance, a challenge all DBAs must face in order to prevent suboptimal execution plans. It continues with a detailed explanation on how to interpret an execution plan. Each aspect of an execution plan will be examined, from cardinality estimates to parallel execution, and you will learn what information you should be gleam from the plan and how it affects the execution performance of a SQL statement. After lunch the workshop focuses on the process of analyzing and resolving the most common SQL execution performance problems including poor cardinality estimations, bind peeking issues, selecting the wrong access method and much, much more.

You can register for the event here. I hope you can join us!

+Maria Colgan

About

The Oracle Optimizer blog is written by members of the Optimizer development team. The goal of this blog is to provide an insight into the workings of the Optimizer and the statistics it relies on. The views expressed on this blog are our own and do not necessarily reflect the views of Oracle and its affiliates. The views and opinions expressed by visitors on this blog are theirs solely and may not reflect ours.

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