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February 2014

New “DBA Kevlar Ammo” Flipboard

A number of folks have told me how much they enjoy the content that I “buffer” out throughout a 24 hr automated period, but hate how much  they often miss vs. getting “spammed” with all of it at once and just being overwhelmed.  I’m trying to find the best of both worlds and have started to push this content out to my very own Flipboard magazine.

CBO Days 2014

CBO Days 2014
Event date: 
Tue, 2014-06-10 - Wed, 2014-06-11

CBO Days 2014

CBO Days 2014
The company I work for, Trivadis, is very pleased to organize, on the 10th and 11th of June, an outstanding seminar with top guest speakers in Zurich. This year’s focus will be on the Oracle query optimizer, also known as a cost-based optimizer (CBO).

The query optimizer is not only one of the most complex pieces of software that constitutes the Oracle kernel; it is also one of the most unappreciated. Why? To make the best and most efficient use of the query optimizer, you definitely need to understand how it works. This is exactly what we are aiming for at the CBO Days.

Enjoy the two days with:

VirtualBox 4.3.8

VirtualBox 4.3.8 has been released. The downloads and changelog are in the usual place. It’s a maintenance release, so lots of bug fixes.

Happy upgrading!

Cheers

Tim…


VirtualBox 4.3.8 was first posted on February 26, 2014 at 6:52 pm.
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Parallel Execution – 4

I’m aware that in the previous article in this series I said I’d continue “in a few days” and it has now been more like 11 weeks – but finally I’ve got the time. In this article I’m going to talk primarily about Bloom filters and their impact on performance, but I’ll need to say something about the “virtual tables” and “parallel execution message size” before I begin. Take a look at this fragment of a parallel execution plan:

Predicate Order

Common internet question: does the order of predicates in the where clause make a difference.
General answer: It shouldn’t, but sometimes it will thanks to defects in the optimizer.

There’s a nicely presented example on the OTN database forum where predicate order does matter (between 10.1.x.x and 11.1.0.7). Notnne particularly – there’s a script to recreate the issue; note, also, the significance of the predicate section of the execution plan.
It’s bug 6782665, fixed in 11.2.0.1

GITHUB_UTL Tutorial 9: Automatic github issues for error tracking.

This is just going to be a short entry. In the last tutorial I showed you how to enable automatic revisioning of all your plsql code in an oracle schema. What you can also do with the github_utl package is setup automatic issue creation for schema errors. This basically means that you will get an issue in the right repository, every time a servererror happens in that schema. This makes it extremely easy to track if there are any logical errors with your code, or if your users are trying to use it the wrong way.

FBI Skip Scan

A recent posting on the OTN database forum highlighted a bug (or defect, or limitation) in the way that the optimizer handles index skip scans with “function-based” indexes – it doesn’t do them. The defect has probably been around for a long time and demonstrates a common problem with testing Oracle – it’s very easy for errors in the slightly unusual cases to be missed; it also demonstrates a general principle that it can take some time for a (small) new feature to be applied consistently across the board.

The index definitions in the original posting included expressions like substr(nls_lower(colX), 1, 25), and it’s possible for all sorts of unexpected effects to appear when your code starts running into NLS  settings, so I’ve created a much simpler example. Here’s my table definition, with three index definitions:

NYC, NYOUG and Delphix on March 12 & 13

 

NYC_thomashawk

photo by Thomas Hawk

Interested in talking face to face about Delphix in NYC?  Drop me a line. I’ll be in NYC on March 12th and 13th and look forward to meeting folks who are excited to learn more about Delphix.

Facebooking the Squarespace Flatiron

Have you built a site on a Squarespace template such as Flatiron or Marquee
supporting the concept of index pages or index collections? Do you post a
page or a gallery link to Facebook only to be...



Read the full post at www.gennick.com/database.