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August 2014

Just Don’t Call It Science!

I’ve had two rather frustrating conversations recently with people who have claimed “science” and “proof” where it is totally inappropriate. One was regarding a 3000 year old religious text. The other was a bunch of medical-related blog posts. In both cases, the people were making very valid points and thought they were backing up their stance with “scientific proof”. The problem was, by inappropriately playing the science card, they made themselves and their beliefs sound stupid. Like I said, in both cases they were making very valid points, but their supporting arguments were just plain dumb!

I really do feel most people out there do not have a clue what science and scientific methods actually are. Just to bring this closer to home, I would just like to make this point. Please read this next line and the following explanation before you feel the need to comment…

Zone Maps

Zone Maps is a new feature that got officially introduced in 12.1.0.2.0 so I've decided to take a closer look.

From the Oracle Documentation:

For full table access, zone maps allow I/O pruning of data based on the physical location of the data on disk, acting like an anti-index.



Let's start by creating a test table:

SQL> create table t pctfree 95 clustering by linear order (n) as
2 select level n, rpad('x', 200, 'x') v
3 from dual
4 connect by level <= 5000;

Table created

I've used a high pctfree setting to make sure the table gets spread out on disk -- each row will occupy it's own block:

SQL> select count(*) num_rows,
2 count(distinct dbms_rowid.rowid_block_number(rowid)) num_blocks
3 from t;

NUM_ROWS NUM_BLOCKS
---------- ----------

In Search of Plan Stability (Part 1) - August 27 webinar

Register by clicking here.

Hope you'll join me!

Why am I seeing “Result: Failed. Insufficient resource available” messages?

This is an interesting point that came up recently, where someone had a DBaaS environment running on an Exadata system for a couple of months, with no issues.  It has recently started to return errors on the Database Cloud Self Service portal in the “Placement Algorithm” region:

Constraint : Number Of Databases
Current Resource Usage: 18
Total Resource Available: 10
Maximum Limit Defined: 10
Requested Value: 1
Total Resource that can be used: 10
Result: Failed. Insufficient resource available.

But if I grep for PMON processes,  the number of databases running on the machine is 8.  Why would I see such an error?

The reason here is fairly simple – there are a couple of databases that are down, and if we include those, the number of databases on the machine has reached the maximum limit defined. But the explanation needs a bit more detail.

Weblogic Start Failure: Empty Initial Replica

This post is to address a failed Weblogic start in EM12c.  The fix is performed on a Windows host, but the fix can easily be for any EM12c environment that experiences this issue.  In the below instructions, just replace the %OMS_BASE% for Windows Env Var to $OMS_BASE for Linux/Unix.

Issue:  OMS Fails to Start and Points to Weblogic Issue in EMGC_OMS1.out File.

Oracle Midlands : Event #5

Just a quick reminder that Oracle Midlands Event #5 is just around the corner (#000000;">Tuesday 16 September).

  • Boost Performance by Clustering Data - Martin Widlake
  • Data Virtualisation and Instant Cloning - Ron Ekins (Delphix)

Martin is always good value, so I’m looking forward to that session. I’ve seen a couple of talks on the Delphix stuff and it is seriously cool! I think this session will open a few people’s eyes… :)

Big thanks to the Red Gate Software folks for sponsoring the event, allowing it to remain free

MERGE and IOT’s ….. unhappy bedfellows

Anyone who has used Oracle for a while will be familiar with the Parent/Child locking "issue" when it comes to tables and indexes on foreign keys.  For many years you’d hear people crying "bug" etc but thankfully most now know the reason, and accept it as sensible behaviour.

But lets take a look at a slight variation on that theme.

Lets start with a table called "LOC" which will be our parent table in this example. Note that it is an IOT, and we’ll also have a child table "LOC_CHILD", which is also an IOT.

Monitoring a Microsoft OS Failover Cluster

I know, I know-  none of you are using Microsoft Windows.  This is why I get so many questions on this topic and why there is so much interest in a white paper that no one thought I needed to write.  Well, while that pesky ol’ white paper is in review, I’m going to go onto a secondary topic of how to monitor a Microsoft Active/Passive cluster with Enterprise Manager 12c, release 4.

In-memory limitation

I’ve been struggling to find time to have any interaction with the Oracle community for the last couple of months – partly due to workload, partly due to family matters and (okay, I’ll admit it) I really did have a few days’ holiday this month. So making my comeback with a bang – here’s a quick comment about the 12.1.0.2 in-memory feature, and how it didn’t quite live up to my expectation; but it’s also a comment about assumptions, tests, and inventiveness.