Monday, November 9, 2009

RMAN Convert database and ORA-7445

Using the CONVERT command in RMAN can be an efficient way to migrate a database from one OS to another, if they have the same endian.

We migrated 9 databases on from HP-UX (on Itanium) to AIX. The databases where distributed on three servers with not exactly the same hardware configuration. On one of the servers we encountered an error described in bug 888530 on Metalink or My Oracle Support. The process terminated prematurely with ORA-7445 when converting an undo tablespace. The other tablespaces were migrated fine, but the undo tablespace ended up with a missing datafile. After the error occurred the RMAN session was left hanging and after killing it the migrated datafile belonging to undo was removed; may be that had something to do with the file system being NFS mounted. Anyway, our solution was to create another undo tablespace and change the undo_tablespace parameter, and then dropping the corrupted one. In one of the tests we did, we managed to do recovery on the migrated undo tablespace, but some funny error messages showed up in the alert log, probably because it was not finally migrated to the new platform. Meaning, if you get this error, create a new tablespace for undo and drop the old one.

Sunday, October 11, 2009

Manually add a host target to Grid Control

Case: I wanted to reinstall the Enterprise Manager agent on a host. I went on to delete the host in the list of targets in EM. Then after a new installation and synchronization I somehow managed to push the list of targets from GC to the agent and thereby removing the host as a target in the local targets.xml file. Result: The monitored host did never show up in the target list of hosts even after a successful installation of the agent.

Solution: Create a temporary file /tmp/newtarget with one line:

<Target TYPE="host" NAME=""/>

Where is the host name. Then add the target with:

emctl config agent addtarget -f /tmp/newtarget

Tuesday, June 2, 2009

AIX and large pages

I'll probably need this in the not-so-distant future. Here is the link to Noon's write-up when I need it. His blog is recommended, by the way.

Sunday, March 8, 2009

Passed the OCP exam

Friday I passed the OCP exam (1Z0-043). In two months I have studied for, and taken three tests in order to achieve OCP certification. Before I started on this in January I had noe previous experience with Prometric testing or certification at all. But I knew I had read a post about it earlier and started looking up an old post by Chen Shapira about how she prepared for the OCA exam. I ordered the same book as well as another book for the test that was added as an extra requirement for the OCA level December last year. I more or less made the same experience that she did, in my words:
  • Working experience with Oracle is very usefull. It helps you remember it all.
  • These exam preparation books are not perfect, but the authors seem to know what is important and not. verifying against the Oracle documentation, other books, and your own experience is important, though.
  • The cd-rom that come bundled with the book is not that usefull. In one of the question the answer is given, the questions seem mixed up between OCA and OCP, and overall did not impress with quality. But it managed to raise my stress level the night before the OCA exam and keeping me alert. Usefull if you've never taken a Prometric test before. But before the OCP test I skipped the test software in order to avoid confusion.
  • Especially when reading for the OCA tests I had the feeling that I knew 95% of the stuff, but the questions in the book revealed to me which concepts that where not completely clear to me. Also one may read it too lightly and not capture important details for trick questions.
  • Check the exam topics at the Oracle site (as of now: OCA topics and OCP topics) and compare it with the preparation book you are reading (if you do). For instance, globalization is not much of a topic for the OCA exam (except that you have to know about setting a few NLS-variables), but it is a topic for the OCP exam. In the book by Watson and Bersinic Globalization is covered in chapter 21 in the OCA part. The topic list also served as check list of what to study the last days before the exam when I had finished reading the preparation book.
  • Getting used to the Prometric testing in itself is important. Pay attention to details in the questions and check the timer once in a while, if you spend too much time in the beginning you may not have enough time at the end. Now that OCA requires an extra test it may be the best opportunity to get used to these tests if you have never taken them before. Exam 051 11g SQL Fundamentals has only 65 questions to be answered in 120 minutes and a passing score of 60% (again, check for changes).
One example of where statements in the preparation book does not agree with other books and documentation I've read can be found on page 812. The exam tip at the end of the page reads:

many people think that a log switch triggers a checkpoint. It doesn't. It used to, but that behaviour changed with release 8i, when incremental checkpointing was introduced...

However on page 100 in Tom Kyte's book "Expert Oracle Database Architecture" second-last paragraph:
Many things can cause a checkpoint to occur, the most common event being a redo log switch.

I'm inclined to believe that Kyte got it right. One is not allowed to report from these exams, but I think it is safe to say that the issue was somehow touched.
The main reason I went for certification was a requirement from at least one of our customers. Now that I'm through it all I am of course contend that I was pushed into it. The certification helps to identify gaps in your knowledge, gaps one may not be aware of even if you have worked with the database for years. One may question what is the use of knowing how to solve the same problem in five different tools.

Being an OCP does not equal being a good DBA, but it looks nice on the CV and quite a few of those requesting a certification do not know what it is all about.

Thursday, February 12, 2009

New job

This year started off fine with a new job. I quit the company I joined just 25 months earlier, in itself a defeat. Though I gained much useful experience there, some signals convinced me to move on, and now I am quite happy that I did so. I joined Steria Norway to work as a senior system consultant, and so far it looks quite promising. The company is internationally focused and one is encouraged to build networks outside one's country, something I find interesting. There is constant pressure to improve; yesterday I finished the second exam in order to achieve my OCA certification (Last December Oracle introduced a second exam as a requirement for the OCA). And I won't stop there.

What else; two weeks ago I gave another thought about using Facebook; understanding that social networking on the net is important I concluded that I should give it another try, and reactivated the account after more than a year off. What matters is probably what one publishes there, and not being there or not. This post has been an exception to my rule; I should get back to writing about the database.