Oracle performance tuning with Real World Performance Group

February 24, 2014 by Leave a comment 

Oracle Real World Performance Tour seminar in Munich

Oracle Real World Performance Tour seminar in Munich

I was a part of a unique Oracle training seminar that happened in Munich, Germany last week.
This is a Day of Real World Performance Tour seminar given by: Andrew Holdsworth, Tom Kyte, Graham Wood. These 3 well known Oracle experts are key members of the Real World Performance Team that consist of about 25 database experts who focus on Oracle database performance tuning, creating live demos and teaching customers how Oracle perform and how they should write the optimal code.

The format of this Oracle event is very unique. The entire seminar day Andrew, Tom and Graham are continuously on stage sharing in the conversational format very unique technical material debating (sometimes in a funny form) with each other and the audience. There are three screens in the seminar room and every instructor drives his own projector. They show the quite interesting live demos loading terabytes of data and manipulating with billions of rows in just several minutes on their own Exadata systems.

Interesting enough that these guys consider performance tuning aspects of the same problem from different angels sometimes contradicting each other but finally giving concrete solutions and best practices to follow. After those tests and lessons learned you definitely change your mind in terms of database and application performance tuning.

This training seminar makes interesting not only the unique technical material but also all three very different personalities of the instructors and their backgrounds. Tom has never been a DBA but he represents mainly Read more »

How CASE expression manipulates with NULL in Oracle SQL

February 4, 2014 by Leave a comment 

My next post is an answer to the below question about Oracle SQL CASE expression and the way how it manipulates with NULL values compared to DECODE function. This topic in fact is very common in Oracle database developers’ area.

===============
Hi Kirill,

Could you please help me to clarify below mention doubt.

DECODE:-

select decode (null,null,’true’,’false’) as value from dual

OUTPUT:- TRUE

CASE:-

select case null when null then ‘true’ else  ‘false’ end as Case_Test from dual

OUTPUT :- FALSE

Why above mention queries are giving different output  and what is the difference between case and decode?

==============

CASE expression treats NULLs in Oracle database SQL a bit differently compared to DECODE. You have to understand that the Boolean expressions usually result in TRUE or FALSE , but NULLs introduce a third possible result which is : UNKNOWN . At the same time NULL is not the same as UNKNOWN. See an example below:

sum + NULL results in NULL (this is a Scalar expression.)
NULL = NULL results in UNKNOWN (this is a Boolean expression.)
sum < NULL results in UNKNOWN (this is a Boolean expression.)

Ok. Now let’s explore the Oracle SQL CASE expression itself.

Oracle database SQL CASE expression

Oracle database SQL – CASE expression

CASE introduces two ways of conditional expressions: Simple CASE and Searched CASE. Read more »

Oracle database housekeeping methods – Unix log rotation

January 10, 2014 by Leave a comment 

Since Oracle Database 11g, all traces, incident dumps and packages, the alert log, Health Monitor reports, core dumps, and more files are stored in the ADR, a file-based Automatic Diagnostic Repository for simplified database diagnostic data management. In spite the housekeeping or purging of those files got not simplified, unfortunately the new Oracle utility ADRCI can not purge all the files that Oracle database generates in ADR. Thus, you should use the other OS methods and tools to accomplish Oracle database housekeeping.

This time I share a method of rotating Oracle database log files using Unix logrotate mechanism. The below example will rotate the Oracle alert.log and listener.log files in the following way:

– Rotation is based on the file size (you can use “M” or “k” for Mb and Kb)
– Unix Logrotate utility creates a copy of the original log file, then truncates it
– The rotated files will be compressed with Unix gzip utility with the following name <logfile>-yyyymmdd.gz
– Only recent 20 rotated log files are kept
– Rotation frequency is default = weekly
– No errors generated if the log file is missing
Read more »

Oracle 11g files housekeeping methods

January 3, 2014 by 2 Comments 

Since Oracle Database 11g, all traces, incident dumps and packages, the alert log, Health Monitor reports, core dumps, and more files are stored in the ADR, a file-based Automatic Diagnostic Repository for simplified database diagnostic data management. However housekeeping or purging of those files got not simplified. Unfortunately the new Oracle utility ADRCI can not purge all the files Oracle database generates in ADR. Thus, you should use the other OS tools to accomplish the same. Below I list common Oracle files that must be cleaned periodically with associated housekeeping methods I usually use on Linux servers.

Logs rotation

– Linux log rotate mechanism used
– alert.log, listener.log, backup logs and any other log files affected
– Files are purged and zipped for archiving purpose

Read more about Oracle database housekeeping using Unix logrotate mechanism.
Read more »

Oracle Exadata X4 database machine – software insights

December 6, 2013 by Leave a comment 

The newest Oracle Exadata Database Machine X4 is available for ordering! After I reviewed in my last article some hardware insights of Oracle Exadata X4, let’s talk about the software options, improvements and new features that will be available soon in the new Exadata.

If you order an Oracle Exadat X4 system you can choose between two Oracle database versions: 11g or 12c.  The relevant database version will be pre-installed by Oracle Advanced Customer Support (ACS) Services with additional Grid infrastructure software including Oracle ASM and RAC. Prerequisite is that you have enough database and RAC licenses.

Oracle Exadata X4 Machine will be delivered with the new Exadata software version 11.2.3.3.0 that provides the following major capabilities:

– Automatic Flash compression on X3 and X4 systems
– Improved support for consolidation of multiple databases
– Many management improvements
– Many robustness and availability improvements

See below some major new Exadata software featurues that are going to be incorporated to the new X4 machines.
Read more »

DBMS Blog Updates : Subscribe RSS RSS: Subscribe to Articles · Subscribe to Comments Subscribe RSS Receive site updates via email