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RAC, parallel query and udpsnoop

I presented about various performance myths in my ‘battle of the nodes’ presentation. One of the myth was that how spawning parallel query slaves across multiple RAC instances can cause major bottleneck in the interconnect. In fact, that myth was direct result of a lessons learnt presentation from a client engagement. Client was suffering from performance issues with enormous global cache waits running in to 30+ms average response time for global cache CR traffic and crippling application performance. Essentially, their data warehouse queries were performing hundreds of parallel queries concurrently with slaves spawning across three node RAC instances.

Of course, I had to hide the client details and simplified using a test case to explain the myth. Looks like either a)my test case is bad or b) some sort of bug I encountered in version c) I made a mistake in my analysis somewhere. Most likely it is the last one :-( . Greg Rahn questioned that example and this topic deserves more research to understand this little bit further. At this point, I don’t have and database is in and so we will test this in


UDP is one of the protocol used for cache fusion traffic in RAC and it is the Oracle recommended protocol. In this article, UDP traffic size must be measured. Measuring Global cache traffic using AWR reports was not precise. So, I decided to use a dtrace tool kit tool:udpsnoop.d to measure the traffic between RAC nodes. There are two RAC nodes in this setup. You can read more about udpsnoop.d. That tool udpsnoop.d can be downloaded from dtrace toolkit . Output of this script is of the form:

Diagnosing and Resolving “gc block lost”

Last week, one of our clients had a sudden slow down on all of their applications which is running on two node RAC environment

Below is the summary of the setup:
– Server and Storage: SunFire X4200 with LUNs on EMC CX300
– OS: RHEL 4.3 ES
– Oracle (database and clusterware)
– Database Files, Flash Recovery Area, OCR, and Voting disk are located on OCFS2 filesystems
– Application: Forms and Reports (6i and also lower)

As per the DBA, the workload on the database was normal and there were no changes on the RAC nodes and on the applications. Hmm, I can’t really tell because I haven’t really looked into their workload so I don’t have past data to compare.

New job, lots of exciting stuff

It’s been a week since I started my new job at Oracle Corporation. I’m a remote worker which means that the first day of work wasn’t the usual event since I just went to my home office and got on a concall with my new manager. After getting connectivity and accounts set up properly, I was able to pretty quickly work through the new hire checklist of forms and mandatory training.

My new Oracle-provided laptop arrived around mid-week and I realized that, at least for now, I’ll have to revert back to using the Windows-based laptop and (hopefully temporarily) put my MacBook Pro on the shelf. Actually, my wife is very excited since she’ll get the MBP to use now and we’ll do the usual “trickle down” to the kids so that the oldest computer in the “fleet” will get ditched.

Yast on OEL

Lately I’ve been playing with Enterprise Manager Grid Control on OEL 4.4 (I’ll upgrade this to soon) and I’ve had a couple of product presentation and demo focusing on the Database Enterprise Management, well among all the packs under this Grid Control “Area” the hottest are the Configuration Management and Data Masking.

Understanding the SCN

For the DBAs who want to have a refreser on SCN (system change number), this article article is very nice and explained clearly written by Sandeep Makol. It started on where you ‘ll find info for SCN (controlfile and datafile headers) then goes to the backup and recovery scenarios where knowledge of this “magic number” is very useful.

Below are some useful scripts (with sample output) as well

Oracle’s latest acquisition: Me

I’m definitely the type of person that gets excited by new opportunities and always loves a new challenge. Without challenge, I get bored quickly and boredom makes me a little crazy.

So, this new opportunity came along a little while ago and I thought it sounded just perfect for me. Many of you that know me will recall that I’ve had trouble finding the right company that fits with all aspects of my personality, goals, and philosophy which has led me to “try” a few of them in the past several years. I don’t regret the choices I’ve made and I’ve learned an awful lot from each of my employers. Most importantly, I’ve created new relationships at each of my past companies that I still maintain today.

Collaborate 09: Don’t miss these sessions

Collaborate 09 starts on Sunday, May 3 (a few days from now!) in Orlando. I’ve been offline for several weeks (more on that later), but will be returning to the world of computers and technology in full force in Orlando. I’ve had a few inquiries about whether or not I’ll be at Collaborate, so I thought I’d resurrect my blog with a post about where I’ll be and some of the highlights I see at Collaborate 09.

First, where I’ll be presenting:

ADV: RAC Attack Hands-on Event at Collaborate09

The RAC SIG, Oracle and IOUG are thrilled to present the hands-on event dubbed “RAC Attack!” at Collaborate09 in Orlando, FL. It is a half-day University Session in the IOUG Forum scheduled for the morning of Thursday, May 7th.

Each participant will have their own private RAC cluster to use. You’ll be able to install a new cluster, test session failover, perform backup and recovery and just about anything else you’d like to try (time permitting). The session will have lab outlines with very specific instructions that cater to beginners. Advanced users are welcome to test anything they like. If you try something that doesn’t work, we have mechanisms in place to help “reset” your cluster in 15 minutes and let you continue working and testing.

New presentation: Simulating failures for testing and diagnostic practice

In this entertaining presentation, Jeremiah Wilton demonstrates creative ways to induce Oracle failures with the objective of learning how to detect, assess and diagnose problems.  Some of the self-induced failures are quite amusing, and will allow the reader to have some fun with their DBA friends.

Check out the presentation on our whitepaper page.

Exadata front and center

Just in case you were like me and did not tune in for Oracle’s quarterly earnings concall, there were some interesting highlights. As many of you (well, there aren’t that many of you that read this, but…) know, I’ve been very interested in Exadata since its announcement at Oracle OpenWorld 2008 in October. While some observed that Larry’s introduction keynote was rather brief, I didn’t take it as a sign of disinterest at all. According to the concall earlier this week, quite the opposite.

Here are some choice excerpts from the transcript that I find telling about the future of Exadata:

Larry Ellison:

“So, that’s looking back. Now looking forward, I think the most exciting product we’ve had in many, many years is our Exadata Database Server.”