Top 60 Oracle Blogs

Recent comments

Performance tuning

Extended DISPLAY_CURSOR With Rowsource Statistics


So this will be my Oracle related Christmas present for you: A prototype implementation that extends the DBMS_XPLAN.DISPLAY_CURSOR output making it hopefully more meaningful and easier to interpret. It is a simple standalone SQL*Plus script with the main functionality performed by a single SQL query. I've demoed this also during my recent "optimizer hacking sessions".

DBMS_XPLAN.DISPLAY_CURSOR together with the Rowsource Statistics feature (enabled via SQL_TRACE, GATHER_PLAN_STATISTICS hint, STATISTICS_LEVEL set to ALL or controlled via the corresponding hidden parameters "_rowsource_execution_statistics" and "_rowsource_statistics_sampfreq") allows since Oracle 10g a sophisticated analysis of the work performed by a single SQL statement.

Troubleshooting ‘DFS lock handle’ waits

Waits for ‘DFS lock handle’ can cause massive performance issues in a busy RAC cluster. In this blog entry, we will explore the DFS lock handle wait event, and understand how to troubleshoot the root cause of these waits. I am also going to use locks and resources interchangeably in this blog, but internally, they are two different types of structures.

A little background

DFS (stands for Distributed File System) is an ancient name, associated with cluster file system operations, in a Lock manager supplied by vendors in Oracle Parallel Server Environment (prior name for RAC). But, this wait event has morphed and is now associated with waits irrelevant to database files also. Hence, it is imperative to understand the underlying details to debug the ‘DFS lock handle’ waits.

How does it work?

Oracle Open World 2011 – My presentation on RAC topic

I will be talking about “Administering Parallel Execution in RAC” with demos on Sunday morning 9AM-10AM (session id 28060). This is part of IOUG RAC SIG presentation series. You would enjoy the content and demos I have prepared.

I know, it is too early, but hoping to see you there!
BTW, if you have attended my RAC Advanced Troubleshooting class series, please don’t hesitate to introduce yourself when we meet.

Session details:
Session ID: 28060
Session Title: IOUG: Administering Parallel Execution in Oracle RAC
Venue / Room: Moscone West- 2005
Date and Time: 10/2/11, 9:00 – 10:00

Update: I just completed this session in IOUG. Thank you for coming, if you were in the room.
You can download the pdf file from
PX execution in RAC

RAC hack session – Tuesday – July 11 2011

I will be conducting a 1-hour deep dive session about RAC LMS process (and about LGWR processes too if time permits) using advanced UNIX utilities. Read Tanel’s blog entry for details:
RAC hack session

See you there!

1-Day Expert Oracle-centric Conference at MIT – 07/07/11 -virtual or physical

You probably aware of 1 day event happening on July 7th Thursday 9AM-5PM EDT (virtually and physically). I will be talking about advanced UNIX tools to debug issues. You can find details of 1-day event here

Here is the outline of my presentation:

Advanced tools and techniques in Unix environment – Riyaj Shamsudeen – 07/07/2011, 3:15pm – 4:00pm EDT

Unix environments provides rich set of tools to debug performance issues. Even if the issue is complex to understand, if we use right tool for the job, we can identify the root cause of an issue quickly. In this presentation, the speaker will demo tools such as truss/strace, pfiles, pmap, prstat, vmstat, mpstat etc to show how you can debug complex issues. The speaker will also introduce Solaris/dtrace to understand performance issues.

Why not join us?

Advanced RAC Training

I will be delivering an intense, advanced 2-week RAC training seminar in Aug 22-26 and Sep 19-23 with numerous demos, dumps and scripts. We will meet 4 hours per day, in a virtual world, 8AM-12 Noon Pacific time for those two weeks. Tanel has written has a great blog post about this seminar series Advanced RAC training.

If you like my presentations about RAC and performance tuning, you will love my seminar series. You will gain better understanding about RAC internals, and you will be able to advance your debugging and performance tuning skills attending my seminar series.

Join me and Let’s explore RAC further.

Presenting in IOUG Webinar: RAC Performance tuning – Private inter connect

I will be presenting in IOUG Webinar on Thursday June 30, 2011 11AM-12Noon CDT. Hope you can join me.
Register at Private interconnect .
I know, I have not been blogging more actively, but I have been working on books and few presentations lately. Hopefully, you will see more blog entries soon.
Thanks for reading my blog.

Books and presentations

As you probably know that my first co-authored book Expert Oracle Practices was released in 2009. I have co-authored one more book Pro Oracle SQL with my esteemed colleagues. This books covers many aspects of better SQL development. Have fun reading :-)

I also will be presenting in few conferences in the upcoming months: RMOUG Training days 2011 , Hotsos symposium ’11, and IOUG Collob . Hopefully, I will see you in one of the conference (or all of the conferences)

Hotsos 2011

I will be talking about advanced RAC troubleshooting in Hotsos symposium ’11. Hotsos Symposium, conducted every March in Dallas, TX, is an intensive seminar series probing the deep waters of Performance related to Oracle Database.

There are many great speakers in this conference. It gives me a great pleasure to meet many folks that I have known for years, exchange ideas, and learn from industry leaders.

Hope to see you there!

Does an UPDATE statement modify the row if the update modifies the column to same value?


If a table column is updated with the same value in a row, does Oracle RDBMS engine modify the data? (or) Does RDBMS engine have an optimization skipping the update, as value of that column is not changing? This was the essence of a question asked in Oracle-l list and I think, it is a good topic for further discussion. Jared Still came up with a fine method to understand this issue measuring redo/undo size. We will explore the same questions with redo log dump method in this blog entry.

Following few lines shows a test case creating a table, an index, and then populating a row in the table.

create table updtest (v1 varchar2(30));

create index updtest_i1 on updtest(v1);

insert into updtest values ('Riyaj');


REDO records and change vectors