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OIC(A) again

Issues with OICA/OIC (OPTIMIZER_INDEX_COST_ADJ/OPTIMIZER_INDEX_CACHING) parameters have already been mentioned many times. Recently I’ve noticed one more and I think I didn’t see this case somewhere else on the Internet so I’ll share it.


Here’s a simple table T1 holding 1M rows with the indexed column X having 10 distinct values:

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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...

PL/SQL procedure successfully completed.

Now let’s “force” the parallel query in my session, run the query and check the execution plan:

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?

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 standard deviation is another brush-stroke toward a fuller picture that will help you draw meaning from the data you're studying.

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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VirtualBox 4.2.10…

Were you thinking, “I’ve got nothing better to do this weekend than to download the latest version of VirtualBox and update the guest additions on all my VMs”? Well your luck is in!

Oracle have just released VirtualBox 4.2.10. The downloads and changelog are in the usual places.

Happy upgrading!

Cheers

Tim…