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March 2013

Alter session force parallel query doesn’t really force anything

Jonathan Lewis has already written about this behavior from the angle of PARALLEL hints.
I’m writing a similar article just because the word FORCE in the ALTER SESSION FORCE PARALLEL QUERY syntax. Force should mean that some behavior would always happen (when possible), right? Let’s test:
SQL> CREATE TABLE t AS SELECT * FROM dba_objects; Table created. SQL> CREATE INDEX i ON t(owner); Index created. SQL> @gts t Gather Table Statistics for table t.

Alter session force parallel query doesn’t really force anything

Jonathan Lewis has already written about this behavior from the angle of PARALLEL hints.
I’m writing a similar article just because the word FORCE in the ALTER SESSION FORCE PARALLEL QUERY syntax. Force should mean that some behavior would always happen (when possible), right? Let’s test:
SQL> CREATE TABLE t AS SELECT * FROM dba_objects; Table created. SQL> CREATE INDEX i ON t(owner); Index created. SQL> @gts t Gather Table Statistics for table t.

Lock Bug

Here’s an oddity that I ran into a little while ago while trying to prepare a sample trace file showing a particular locking pattern; it was something that I’d done before, but trace files can change with different versions of Oracle so I decided to use a copy of 11.2.0.2 that happened to be handy at the time to check if anything had changed since the previous (11gR1) release. I never managed to finish the test; here are the steps I got through:

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.