Pythian Group

Oracle ASM 11g Release 2 – The Evolution

Oracle Automatic Storage Management has proven to be one of the most widely adopted new features in Oracle Database 10g and it has been dramatically improved in the later 11g releases. This presentation will explain what changes are solved by ASM, how these challenges are solved, what barriers there are to ASM adoptions, and how 11g Release 2 addresses these barriers.

I shall say that the slides alone are not that helpful without my commentary but if you didn’t manage to attend it on one of the previous conferences, we will be releasing it as a webinar soon so stay tuned.

A data file is considered unrecoverable if an unrecoverable operation has been performed on an object residing in the data file since the last backup of the data file. Operations will become unrecoverable if they are not logged in the redo log. These “nologging” operations that suppress the generation of redo log, include the following:

1. direct load/SQL load
2. direct-path inserts result from insert or merge statement
3. ALTER TABLE commands
4. CREATE and ALTER INDEX commands
5. INSERT /*+APPEND*/
6. partition manipulation
7. database object that has explicitly set with nologging option
8. Oracle eBusiness Suite concurrent job execution identified in Oracle metalink note: 216211.1
9. Oracle eBusiness Suite patches activities that involve database object manipulation

The database recovery operations will look completed, but those data blocks used by the nologging objects in the data file will be marked corrupted when they are recovered. Accessing those nologging data objects in the recovered database instance will return a data block reading error such as ORA-1578 and ORA-26040, and the logical corruption in the data file will prevent the database object from being useful in the recovered database instance.

How do we detect unrecoverable operations?

Unrecoverable data files are those that involve nologging operations since the last successful backup took place. There are several ways to identify them. Read the rest of this entry . . .

Oracle has just released their January installment of their critical patch update (CPU). Vulnerability CVE-2010-0071 is particularly critical, with a CVSS score of 10, the highest possible. It’s a remotely-exploitable listener vulnerability that’s particularly severe on Windows platforms.

Full details are on Oracle’s security site.

I recently performed a migration from Oracle 10gR2 on Solaris to the same version on Linux, immediately followed by an upgrade to 11g. Both platforms were x86-64. Migrating to Linux also included migrating to ASM, whereas we had been using ZFS to hold the datafiles on Solaris. Restoring files into ASM meant we would have to use RMAN (which we would probably choose to use anyway).

As with many databases, the client wanted minimal downtime. It was obvious to us that the most time-consuming operation would be the restore and recovery into the new instance. We were basically doing a restore and recovery from production backups and archived redo logs. It quickly dawned on me that we could start this operation well before the scheduled cutover time and downtime window, chopping at least six hours from the downtime window. The client would only need to keep the new instance in mount mode after the initial restore/recovery finished, periodically re-catalog the source instance’s FRA (which was mounted via NFS), and then re-run the recover database command in RMAN. Once the time comes to cutover, simply archivelog current the original instance and shutdown immediate. Then open the new instance with the RESETLOGS option, and voila! Migration complete!

I’ll try to recreate a simple example here. Read the rest of this entry . . .

About six months ago, the question of storing images in a database came up. This is one of my favorite topics, and has many database-agnostic parts.

Personally, I think “tell me about storing images in a database” is actually a great interview question, because you will be able to see the difference between someone who has just memorized “what’s right” versus someone who is really thinking. It also helps you see how someone will communicate — if they just say “NEVER do it, it’s as bad as crossing the streams!” then they are a type of person that gives you a short answer, without much explanation, and without many nuances. (That may be what you are looking for, but usually you want someone who gives reasons for why they strongly feel one way or another).

Consider the following cases:
Read the rest of this entry . . .

Recently, a customer request came in to limit the runtime of a query in a 10g database for a certain user. But since connection pooling was being used, the session itself should NOT be killed.

Now, why would somebody ask for that?

I think a reason to implement such a restriction is, for example, if a website application requests data from the database and the query takes too long, then the user sitting in front of the web browser cancels the request, and so it would be beneficial to also cancel the query and not have it still running in the background. There might be quite a few other reasons why such restrictions should be implemented.

Anyway, so what would be the best solution for this? The Resource Manager, a feature not too often used in Oracle.

Actually, “overlooked” might be the better word—overlooked when investigating performance problems. I imagine it must be a new DBA’s nightmare to be confronted with end user complaints of “bad performance”, only to find after a long search that the Resource Manager has restricted the CPU for a specific user.

But back to the topic. Resource Manager not only allows one to define how much CPU a certain user or group gets, it also lets one switch into lower priority groups and kill a query while leaving the session running. It is like running a SELECT statement in sqlplus, and pressing ctrl-c. The session is still alive, yet the query is canceled.

Sure, the Resource Manager is documented by Oracle, but when I started to test this feature, I came across a few very interesting things that are not as well documented, and that’s what prompted me to write this post:

Read the rest of this entry . . .

When we founded Pythian Europe a year ago, we had, as former Oracle employees, a rather black-and-white view of the database world. There was the Oracle database; and then “The Others.”

Here at Pythian, though, we learned that the database world is more colorful than that, and very dynamic. Of course there are passionate debates between our Oracle, MySQL, and SQL Server teams over whose DBMS is better. These discussions, however, are friendly and respectful, and when it comes to a concrete situation, the winner is always the customer—his or her business needs and circumstances decide.

We learned a lot about the fascinating history of MySQL and more details about its features from Nicklas Westerlund and Danil Zburivsky, MySQL experts and members of Pythian Europe. Nicklas helped with the migration of a 1 TB Oracle RDB database on OpenVMS to MySQL on Linux. And there’s our Australian colleagues—see Alex’s blog about the Australian Webinar.

Paul Vallée, Pythian’s founder and Executive Chairman really opened our eyes. Paul talks about Oracle’s 11G features with the same enthusiasm he has for MySQL’s federated architecture, or for SQL Server’s peer-to-peer replication technology. You could hardly find anybody who presents his visionary views of the new technology trends like cloud computing, virtualization, or server consolidation with such a deep understanding of the topics.

Here is your opportunity—especially those of you in Europe,the Middle East, or Africa—to confer with Paul Vallée on Thursday, June 4, 2009 12:00 PM–1:00 PM CEST (11AM–12:00 PM GMT) in a free webinar, Database Platform Migration. Read the rest of this entry . . .

Yesterday, The Pythian Group issued a press release about my book, Pythian’s partnership with Sun, and our new “MySQL Adoption Accelerator Package”. I am not a marketing guru, but I can tell you what we the package means in terms of new work that the MySQL teams have been doing.

Basically, the MySQL Adoption Accelerator Package combines customized training with a comprehensive audit of systems. The name “Adoption Accelerator” makes it sound like it’s only for new applications that are almost ready to go live. What the program actually does is have us evaluate your systems, and intensively train you in the areas you want and need. The program is designed to suit all your needs, whether it’s teaching you about one topic (say, query optimization) or an entire range of topics, from Architecture to ZFS (special issues with running MySQL on ZFS, that is, but that did not fit a cute “from A-Z” model…).

Whether you have already adopted MySQL or are thinking of converting from Oracle, DB2, Microsoft SQL Server or even sqlite, this new package may be what you need.

And now, the full text of the press release, for the curious:

‘MySQL Administrator’s Bible’ Hits the Bookstands: Pythian Launches MySQL Accelerator Adoption Package

The Pythian Group, the leading provider of remote database services, is pleased to announce that the much-anticipated MySQL Administrator’s Bible, written by employee Sheeri K. Cabral, is now available.
Read the rest of this entry . . .

On a recent Monday, I had to perform an emergency Oracle standby switchover for a client whose primary instance host had mysteriously rebooted itself over the previous day. Confidence in that host was, understandably, shaken.

The Oracle Data Guard configuration is a 3-instance setup using Data Guard Broker: one primary, we’ll call it OraA, feeding two standby instances, OraB and OraC. In this particular configuration, we perform switchovers between OraA and OraC. Caught in the middle is OraB, which is on a 60-minute standby delay.

After this particular switchover, OraB started complaining with this message in the alert log:

Read the rest of this entry . . .

This is an issue that keeps rearing its ugly head over and over again, and since it greatly affects performance, it is most important that DBAs of any DMBS running on Linux come to grips with it. So I decided to do some research and try different settings on my notebook. Here are my findings.

What can you find on the web?

A Wikipedia search for the word swappiness will come up empty (any volunteers out there want to write an article?). A Google search will show some pretty old material—the best article I found is from 2004: Linux: Tuning Swappiness. This article includes a detailed discussion with some interesting remarks by Andrew Morton, a Linux kernel maintainer.

So, what is swappiness?

Read the rest of this entry . . .