oracle performance

It is probably easy to calculate hourly redo rate or daily redo rate using AWR data. For example, my script awr_redo_size.sql can be used to calculate daily redo rate, and awr_redo_size_history.sql can be used to calculate hourly redo rate. Hourly redo rate is especially useful since you can export to an excel spreadsheet, graph it to see redo rate trend.

Introduction to Direct Mode Writes

Direct mode operations write directly in to the database file skipping buffer cache. Minimal redo(aka invalidation redo) is generated, if the database is not in force logging mode. Keeping the database in no force logging mode is peachy as long as you don’t use Data guard, Streams, or Golden Gate.

This video was created circa July 2011. Click the Read More link to review the video. Version Oracle Database 11.2.0.2

Synopsis: Essentially, we probe the importance of LMS processes using DTrace. Explain why LMS should run in elevated priority. How to review deep statistics about LMS processes and much more.

In this blog entry, we will explore the wonderful world of SCNs and how Oracle database uses SCN internally. We will also explore few new bugs and clarify few misconceptions about SCN itself.

What is SCN?

SCN (System Change Number) is a primary mechanism to maintain data consistency in Oracle database. SCN is used primarily in the following areas, of course, this is not a complete list:

On February 14-16, I’ll be at the Colorado Convention Center in Denver, Colorado for RMOUG’s Training Days Conference. This is the largest regional Oracle User Conference in North America and attracts presenters from all around the country and the globe. I’ll be presenting:

Presentation Name: Troubleshooting RAC Background Process

Abstract: RAC background process performance is critical to keep the application performance. This session will demo techniques to review the performance of RAC background processes such as LMS, LMD, LMON, etc. using various statistics and UNIX tools. The presentation will also discuss why certain background processes must run in higher priority to maintain the application performance in RAC.

Presentation Name: A Kind and Gentle Introduction to RAC

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?

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

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!

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.

Introduction

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');

commit;

REDO records and change vectors

Introduction

In RAC, CSSD processes (Cluster Services Synchronization Daemon) monitor the health of RAC nodes employing two distinct heart beats: Network heart beat and Disk heart beat. Healthy nodes will have continuous network and disk heartbeats exchanged between the nodes. Break in heart beat indicates a possible error scenario. There are few different scenarios possible with missing heart beats:

1. Network heart beat is successful, but disk heart beat is missed.
2. Disk heart beat is successful, but network heart beat is missed.
3. Both heart beats failed.

In addition, with numerous nodes, there are other possible scenarios too. Few possible scenarios: