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March 2018

Improve Data Clustering on Multiple Columns Concurrently (Two Suns in the Sunset)

I’ve had a couple of recent discussions around clustering and how if you attempt to improve the clustering of a table based on a column, you thereby ruin the current clustering that might exist for a different column. The common wisdom being you can only order the data one way and if you change the […]

Comparing Plans

It can be difficult to find the critical differences when comparing execution plans when you want to find out why the optimizer has changed its choice of plan and what may have happened to cause the change, and even the various diff_plan_xxx() functions in dbms_xplan don’t help very much, so I thought I’d write up an example that appeared recently on the ODC database forum to give people some ideas about how to approach the problem. There is, however, no simple algorithm that you can apply to narrow your focus down to the most probable cause of change, there are simply a few methods that have to be applied with a little flair and imagination.

Cool stuff with partition elimination

Sometimes in the IT world, the term “surprise” is not a good one.

“I woke up this morning and got a surprise…my database was down.”

“I ran a SELECT COUNT(*) on my most important table, and got a surprise result of zero rows.”

and so forth. Generally as IT professionals, encountering the unexpected is not a good start to the day Smile.

18c PDB switchover

In multitenant, the recovery and availability are at CDB level. But customers asked for a switchover at PDB level so Oracle has done that in 18c, based on refreshable PDBs.

For this test I have two multitenant database on an Oracle Cloud service in 18c: CDB1 and CDB2. The only special thing I did was disable the mandatory TDE encryption, because I was not able to have the switchover working. With TDE encryption, I got the “ORA-46697: Keystore password required”. But there is no ‘keystore identified by’ option in the ‘alter pluggable database’. Then If you came upon this post from a search on this error, I’ve no solution yet (SR 3-17001228251 opened on the Oracle Cloud Support – see update at the end of the post when solved).

Where in the World Has Goth Geek Girl Been

I’m on track to fly home tomorrow, March 11th after nine days and three events.  I’m pretty exhausted and just ready to go home and catch up on some sleep…:)

I started out last weekend in Victoria BC and was thrilled to be on this emerald island of the Pacific Northwest.  British Columbia is gorgeous as it is, but Victoria is a special place that quickly became one of my favorite places in the world.

Enabled, Accepted, Fixed SQL Plan Baselines

When the documentation is not always clear, I prefer to build a test case to be sure about the behavior in different context and different versions. Here is a test on SQL Plan Management to show which plan is chosen among the different states of SQL Plan Baselines: Enabled, Accepted, Fixed. Thanks to Oracle ACE program, I have some Oracle Cloud credits to quickly provision a database, so I tested that on Oracle 18c.

For this test, I’ve created a table:

create table DEMO as select rownum n from xmltable('1 to 10000');

with 8 indexes:

exec for i in 1..8 loop execute immediate 'create index DEMO'||i||' on DEMO(n,'||i||')'; end loop;

and a procedure to query it several times, setting random costs for the indexes, with only one cheapest:

create or replace procedure runplans(n number) as
dummy number;
begin

Video demo of creating test data using TESTDATA_NINJA

First quick video demonstrating what my test data package can do.

Video demo of creating test data using TESTDATA_NINJA

First quick video demonstrating what my test data package can do.

Friday Philosophy – Explaining How Performance Tuning Is Not Magic?

Solving performance issues is not magic. Oh, I’m not saying it is always easy and I am not saying that you do not need both a lot of knowledge and also creativity. But it is not a dark art, at least not on Oracle systems where we have a wealth of tools and instrumentation to help us. But it can feel like that, especially when you lack experience of systematically solving performance issues.

Create your Oracle test data using JSON and PLSQL

For a long time the only way to create a generator using the testdata_ninja package, was using a pure text
based syntax. It was using special characters and was maybe a bit obscure and not user friendly. The reason for this
was that the databases I needed this package on, was running Oracle 10 and 11. So I needed the package to be compatible
with those versions, and JSON is not supported natively. Looking at the requirements, it would be a good fit for JSON
though. So recently when I needed to run this on Oracle version 12, I had the chance to finally add JSON support. It makes
it a lot more easy to write the generator definitions, as you can see in the below examples.