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DOAG Exaday 2017: a preview

I am quite excited to have been accepted to speak at the upcoming DOAG Exaday taking place June 20 in Frankfurt. It is the third time I have been lucky enough to present at the event, having spoken both in Frankfurt in Hamburg in previous years.

As you can probably imagine by looking at this weblog, I am a great supporter of the Oracle Engineered Systems community. My interest is not limited to Germany: I still remember the many great meetings in London in the context of UKOUG’s Exadays. I am also very lucky to work for @enkitec where we have been sharing real-world experience at E4 for years and will do so again in June this year.

A quick look at Oracle 12.2 performance instrumentation

Thanks to the prep-work done by Andy Colvin, who continuously and boldly goes where no man has gone before, one of our Exadata systems in the lab is now fully upgraded to It comes fully equipped with the matching cellos to support all the cool new features. Exciting times!

The reason for this post is simple: I have started working on our talk for @Enkitec’s E4 conference in June but thought I’d share this little article with you as a teaser :) There might be one or two more of these posts but if you want the full story make sure you catch us (online) during the conference.

Starting an instance with sqlplus and running into ORA-27302: failure occurred at: skgpwinit6

Recently I was applying the data dictionary part from an (exadata bundle) patch and ran into the following errors:

Oracle database (januari 2017 PSU) and TDE wallets

Recently, I was trying to setup TDE. Doing that I found out the Oracle provided documentation isn’t overly clear, and there is a way to do it in pre-Oracle 12, which is done using ‘alter system’ commands, and a new-ish way to do it in Oracle 12, using ‘administer key management’ commands. I am using version, so decided to use the ‘administer key management’ commands. This blogpost is about an exception which I see is encountered in the Januari 2017 (170117) PSU of the Oracle database, which is NOT happening in Oracle 12.2 (no PSU’s for Oracle 12.2 at the time of writing) and Oracle April 2016 and October 2016 PSU’s.

In order to test the wallet functionality for TDE, I used the following commands:

Oracle 12.2 wait event ‘PGA memory operation’

When sifting through a sql_trace file from Oracle version 12.2, I noticed a new wait event: ‘PGA memory operation’:

WAIT #0x7ff225353470: nam='PGA memory operation' ela= 16 p1=131072 p2=0 p3=0 obj#=484 tim=15648003957

The current documentation has no description for it. Let’s see what V$EVENT_NAME says:

SQL> select event#, name, parameter1, parameter2, parameter3, wait_class 
  2  from v$event_name where name = 'PGA memory operation';

------ ------------------------------------- ---------- ---------- ---------- ---------------
   524 PGA memory operation                                                   Other

Well, that doesn’t help…

SLOB 2.3 Data Loading Failed? Here’s a Quick Diagnosis Tip.

The upcoming SLOB 2.4 release will bring improved data loading error handling. While still using SLOB 2.3, users can suffer data loading failures that may appear–on the surface–to be difficult to diagnose.

Before I continue, I should point out that the most common data loading failure with SLOB in pre-2.4 releases is the concurrent data loading phase suffering lack of sort space in TEMP. To that end, here is an example of a SLOB 2.3 data loading failure due to shortage of TEMP space. Please notice the grep command (in Figure 2 below) one should use to begin diagnosis of any SLOB data loading failure:

GTT and Smart Scan – the importance of the append hint

While writing the previous two posts about GTTs and Smart Scan, I stumbled across an interesting observation. When I started putting my thoughts to (virtual) paper, I thought it was going to be a short post. Well, it wasn’t to be, again. Anyway, you might find this interesting.

Initial Situation

If you read the previous posts this code example I used to populate the GTT might look familiar:

insert /*+ append */ into gtt select * from t4 where rownum < 400000;

In situations like this where I’m moving data I developed a habit of using the append hint. I guess I’ve been working on HCC tables a bit too much and therefore didn’t even make a conscious decision to use that hint. It was the right thing to do, as you will see next.

The full test harness is shown here again for reference:

Smart Scanning GTTs – what about Flash Cache?

Continuing the example of the previous blog post (is it possible to Smart Scan GTTs?), I am investigating if Smart Scans against GTTs can benefit from Flash Cache, or “optimised reads”. The easiest way to see this in your session is to calculate the change in session counters based on v$mystat or v$sesstat. Other tools might also provide information about the amount of data read from Flash Cache, but there are quite often extra licenses required …

Little things worth knowing: Can I Smart Scan a Global Temporary Table?

A question that has come up while preparing to deliver another Exadata Optimisation Class is whether you can offload queries against Global Temporary Tables (GTT) or not. There are subtle differences between heap tables and GTTs such as how statistics are handled and where they are stored that merit a little investigation.

I have used the lab environment on the X3-2 (Exadata, RDBMS) to test if I can Smart Scan GTTs. There are some enhancements in 12c regarding GTTs that are mentioned on the Optimiser blog here:

The Setup

Advanced Oracle memory profiling using pin tool ‘pinatrace’

In my previous post, I introduced Intel Pin. If you are new to pin, please follow this link to my previous post on how to set it up and how to run it.

One of the things you can do with Pin, is profile memory access. Profiling memory access using the pin tool ‘pinatrace’ is done in the following way:

$ cd ~/pin/pin-3.0-76991-gcc-linux
$ ./pin -pid 12284 -t source/tools/SimpleExamples/obj-intel64/

The pid is a pid of an oracle database foreground process. Now execute something in the session you attached pin to and you find the ‘pinatrace’ output in $ORACLE_HOME/dbs: