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Nice Additions For Troubleshooting

This is just a short note that Oracle has added several nice details to and respectively that can be helpful for troubleshooting.

ASH, PGA Memory And TEMP Consumption

Since the V$ACTIVE_SESSION_HISTORY view (that requires Enterprise Edition plus Diagnostic License) contains the PGA_ALLOCATED and TEMP_SPACE_ALLOCATED columns.

In particular the latter closes an instrumentation gap that always bothered me in the past: So far it wasn't easy to answer the question which session used to allocate TEMP space in the past. Of course it is easy to answer while the TEMP allocation was still held by a session by looking at the corresponding V$ views like V$SORT_USAGE, but once the allocation was released answering questions like why was my TEMP space exhausted three hours ago was something that couldn't be told by looking at the information provided by Oracle.

Index Scan with Filter Predicate Based on a Subquery

Most execution plans can be interpreted by following few basic rules (in TOP, Chapter 6, I provide such a list of rules). Nevertheless, there are some special cases. One of them is when an index scan, in addition to the access predicate, has a filter predicate applying a subquery.

The following execution plan, taken from Enterprise Manager 11.2, is an example (click on the image to increase its size):
Execution Plan

Challenges and Chances of the 11g Query Optimizer

Challenges and Chances of the 11g Query Optimizer is the name of a presentation I gave at several events (e.g. Trivadis Performance Days, Oracle OpenWorld, DOAG Konferenz, UKOUG Conference) throughout 2011. Its abstract is the following:

With every new release, the query optimizer is enhanced. Oracle Database 11g Release 1 and Release 2 are no exception to the rule. Specifically, they introduce key improvements in the following areas: indexing, optimization techniques, object statistics and plan stability. The aim of this presentation is to review the new features from a practical point of view as well as to point out challenges related to them. In other words, to let you know what you can expect from the query optimizer when you upgrade to Oracle Database 11g.

SQL Trace and Oracle Portal

Recently I was involved in a project where I had to trace the database calls of an application based on Oracle Portal 10.1.4. The basic requirements were the following:

  • Tracing takes place in the production environment
  • Tracing has to be enable for a single user only
  • Instrumentation code cannot be added to the application

Given that Oracle Portal uses a pool of connections and that for each HTTP call it can use several database sessions, statically enable SQL trace for specific sessions was not an option.

Fedora 16 and Oracle…

Fedora 16 came out yesterday and since it’s my main server OS it’s been upgrade crazy round here. All new installs and upgrades were straight forward. No real dramas at all (touch wood).

As usual, I’ve done the OS installation and Oracle installation articles.

Debugging PL/SQL and Java Stored Procedures with JPDA

In 2003 I published a paper entitled Debugging PL/SQL and Java Stored Procedures with JPDA. Its aim was to describe how to debug PL/SQL and Java code deployed into the database with JDeveloper 9i. Two weeks ago a reader of my blog, Pradip Kumar Pathy, contacted me because he tried, without success, to do something similar with JDeveloper 11g, WebLogic 11g and Oracle Database 11g. Unfortunately I was not able to help him. The reason is quite simple, since 2004 I’m an Eclipse user…

Few days later Pradip contacted me again to let me know that, at last, he succeeded. Here you find his notes…

  1. Grant the required privileges
  2. GRANT DEBUG CONNECT SESSION to &&schema_name;

Ad: Der Oracle DBA – Handbuch für die Administration der Oracle Database 11gR2

Der Oracle DBA

The book Der Oracle DBA (Hanser, 2011), which was written in German, is at last available!

I say “at last” because the authors worked on this project for not less than two years.

Exadata Smart Flash Logging Explained

I’ve seen some posts on the blogosphere where people attempt to explain (or should I say guess) how Exadata Smart Flash Logging works and most of them are wrong. Hopefully this post will help clear up some the misconceptions out there.

The following is an excerpt from the paper entitled “Exadata Smart Flash Cache Features and the Oracle Exadata Database Machine” that goes into technical detail on the Exadata Smart Flash Logging feature.

Oracle Database on Oracle Linux 6.1…

I mentioned the day before Open World I put a Virtual RAC on Oracle Linux 6.1 article live. Although the procedure was complete, some of the screen shots were from an old article as I didn’t have time to redo them before my flight. :) I’ve just run through the procedure again and taken new screen shots. As a result, I’ve allowed the article to display on the front page of the website, which is why you will see it listed as a new article there.

This kinda rounds out the whole Oracle on 6.1 stuff as there has been a single instance installation guide out for ages and more recently the Cloud Control installation, which references it.

Remember, it’s still not certified yet, but it’s coming.



Oracle Database 11gR2 on OL6 / RHEL6: Certified or Not?

There seems to be a little confusion out there about the certification status of Oracle Database 11gR2, especially with the release of the patchset which fixes all the issues associated with RAC installs on OL/RHEL 6.1.

Currently, 11gR2 is *NOT* certified on OL6 or RHEL6. How do I know? My Oracle Support says so! Check for yourself like this:

  • Log on the My Oracle Support (
  • Click the “Certifications” link.
  • Type in the product name, like “Oracle Database”
  • Select the product version number, like “″.
  • Select the platform, like “Linux x86_64″ or a specific distro beneath this.
  • Click the “Search” button.

From the results you will see that Oracle Database is certified on OL and RHEL 5.x. Oracle do not differentiate between different respins of the major version. You will also notice that it is not currently supported on OL6 or RHEL6.

Having said that, we can expect this certification really soon. Why? Because Red Hat has submitted all the certification information to Oracle and (based on previous certifications) expects it to happen some time in Q4 this year, which is any time between now and the end of the year.

With a bit of luck, by the time I submit this post MOS certification will get updated and I will happily be out of date… :)