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March 2013

Standard Deviation and the Mean

I've just put up the second in an ongoing series (I hope!) of articles on Oracle SQL's build-in statistical functions. The topic is standard deviation. The previous one, my first, is on the mean. Here are links to the two:
 
2. STDDEV: Standing Sentinel on Your Data
 
1. AVG: What Does it Mean?

10053 Trace Files - Different Plan in Different Environments

Rather than just describing the contents of the trace file, I thought it might be a good idea to tie the various sections into how they might help you solve Real WorldTM problems. Which might not be immediately obvious when the first example I use is the trace file for :- 

SELECT * FROM DUAL;

But here it is. The first thing to note is that it's a 66KB file of over 2000 lines, even for something so trivial, which is just a taste of just how massive these files can be. It will also be environment and version-specific, as you'll see. Such is the nature of low-level trace files.

Going through the initial sections at a very high level, we have ....

Lines 1-20
- The standard type of trace file pre-amble that you might have seen in other trace files including

- The trace file name

Big Data is the Commercial Supercomputing in the Age of Datafication

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id="attachment_53081" style="width: 160px" class="wp-caption alignleft">NERSC's Hopper NERSC; Design: Caitlin Youngquist/LBNL Photo: Roy Kaltschmidt/LBNL
class="wp-caption-text">NERSC’s Hopper NERSC; Design: Caitlin Youngquist/LBNL Photo: Roy Kaltschmidt/LBNL

Delphix Debrief

I’ve had my week in Palo Alto with the Delphix people. I really don’t know where the time went to – but I had a lot of interesting conversations with a number of very able people; plenty of time to experiment; and I’ve even been able to install Delphix on my laptop (as a 64-bit Open Solaris 10 VM under VMWare). I liked the product, and I was impressed with the team they’ve got working on it.

We’ve pencilled in an intial online webinar for Friday 5th April which will probably feature an informal chat where Kyle Hailey and I talk about my impressions of the product and what I’ve done with it so far. Then, in about a month’s time, we’ll have a more technical discussion.

In the meantime, it occurred to me that my next blog post ought to be about LOBs as this would be a nice way to introduce you to one of the key ideas behind DxFS (the Delphix-extended file system that’s based on ZFS).

10053 Trace Files - Getting Started

Before getting into the contents of a 10053 trace file and looking at any useful stuff, you need to know what the files are for and how and where they are created.

10053 Trace Files

Sometimes I'm really not sure whether a blog post is a good idea or not. This is one of those times.

asqlmon.sql: SQL Monitoring-like execution plan line level drilldown into SQL response time

I don’t have much time for a thorough blog post, so I’ll just paste in an example output of my asqlmon.sql script, which uses ASH sql_plan_line columns for displaying where inside your execution plan response time has been spent. Why not just use Oracle’s own SQL Monitoring reports? Well, SQL monitoring is meant for “long running” queries, which are not executed very frequently. In other words, you can’t use SQL Monitoring for drilling down into your frequently executed OLTP-style SQL. I am copying my recent post to Oracle-L mailing list here too:

The main performance impact of the old GATHER_PLAN_STATISTICS / statistics_level = ALL instrumentation came from the fact that expensive timing (gettimeofday()) system calls were used for getting A-Times of row sources.

STDDEV: Standing Sentinel on Your Data

Oracle Database implements a family of STDDEV functions for computing the
standard deviation from the mean. If you think of the mean as beginning to
paint a picture of the underlying data, then...



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

STDDEV: Standing Sentinel on Your Data

Oracle Database implements a family of STDDEV functions for computing the
standard deviation from the mean. If you think of the mean as beginning to
paint a picture of the underlying data, then...



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

AMIS Masterclass – Two Day Masterclass with Oracle ACE Director James Morle

AMIS is spending a lot of effort keeping our people up-to-date with the latest knowledge needed to help our customers the best way we can. Traditionally we also always try to share our knowledge with customers and others, via social media or conferences, and while abroad learning from others at the same time. It is …

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