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Solaris Eye for the Linux Guy… Part III (hugepages = ISM)

This post has been a long time coming but recently, I have started working on some SPARC SuperCluster POC’s with customers and I am getting re-acquainted with my old friend Solaris and SPARC.

If you are a Linux performance guy you have likely heard of HugePages.   Huge pages are used to increase the performance of large memory machines but requiring fewer TLB‘s .  I am not going to go into the details TLB’s, but every modern chip supports multiple memory page sizes.

So how do you get huge pages with Solaris?

Do nothing – it is the DEFAULT with Oracle running on Solaris.

Detective? Crime Writer? DBA? Which are you?

The DBA role can sometimes feel like a mix of detective, crime writer and DBA all thrown together. What do I mean by that? When you hit some problems you have to play detective, trying to find clues to what is going on. Once you’ve started to gather clues, you have to play crime writer and put them together to form a coherent story that explains what is going on. Once you have the outline of your crime story you can start looking at the facts again and see if they fit with your story. If they do, your story may just be correct. If they don’t, you probably need to check the accuracy of the facts and do some rewriting of the story until the two things fit together. Once things seem to fit, you can then get busy trying to arrest the villain, or fix the problem.

Java 7 EE Launch : June 12th & 13th

The Oracle ACE program recently invited members to a teleconference session about the upcoming launch of Java 7 EE. Arun Gupta took us through a preview of the information that will be available to everyone as part of the launch.

If you are interested in getting the low down on this new release, you can register for the launch events here.



BGOUG Spring 2013 : Photos

I was a little bit rubbish and forgot to get photos of the recent BGOUG event. Fortunately, the conference photos have arrived. You can check them out here.

There are a number of photos of an old fat guy that looks a little like me. I don’t remember meeting him though. Weird… I think he needs the toilet in this shot.

Forcing Smart Scans on Exadata – is the _serial_direct_read parameter safe to use in production?

One of the most common Exadata performance problems I see is that the direct path reads (and thus also Smart Scans) don’t sometimes kick in when running full scans in serial sessions. This is because in Oracle 11g onwards, the serial full segment scan IO path decision is done dynamically, at runtime, for every SQL execution – and for every segment (partition) separately. Whether you get a direct path read & smart scan, depends on the current buffer cache size, how big segment you’re about to scan and how much of that segment is actually cached at the moment.

How to hint

Here’s a live example demonstrating a point I’ve often made – you have to be very detailed in your hinting or Oracle will find a way to obey your hints and do the wrong thing.  A recent posting on the OTN database forum gave use the following query and execution plan:

CUR Gets

Here’s an interesting anomaly from the OTN database forum – PL/SQL track. It’s a single row delete from a table that does a huge number of db block gets and (in the first example shown) physical reads. Here’s the supplied output with autotrace enabled:

Debugger Dangers – Part 2

About 5 years ago I wrote about the risks that connecting to Oracle processes via debuggers may cause and what are (in my opinion) the safer and less safer options for taking stack samples from running Oracle processes.

In the end of that article I listed different options for getting a stack traces and whether they were safe or not.

For example, ORADEBUG-based process stack traces (DUMP ERRORSTACK, SHORT_STACK and event the process/system state dumps (at level 256 or higher) are not 100% safe – because they alter the execution path of the process they attached to. Your process may crash or get some error if you hit a bug (of course once you patch/fix the bug, you’ll be fine again – until you may hit the next bug).

An example bug is this:

List Exadata Storage Cell disk summary with cellpd.sql and cellpdx.sql scripts

In the previous post I explained how to list Exadata disk layout and topology details with the exadisktopo scripts, in this post I’ll introduce one celldisk overview script, which I use to quickly see the celldisk configuration, specs and error statuses. The cellpd.sql script (Cell Physical Disk) will show the following output:

List Exadata Disk Layout and Topology with the exadisktopo scripts

Here are two more Exadata scripts for listing the end-to-end ASM<->Exadata disk topology from V$ASM_ views and from V$CELL_CONFIG. These scripts see both the ASM level layout and the storage cell-level disk topology.

The exadisktopo.sql script shows all disks starting from the ASM diskgroup layer, going deeper and deeper all the way to the OS disk device level in the storage cells. It uses outer joins, so will show celldisks even if there are no corresponding grid disks allocated on them (or if there are no ASM disks using them). It also shows the Flash cards used as flash cache, thus there are no ASM disks on them usually.