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November 2011

Mike Carey: Dead Men’s Boots…

Number 3 in the Felix Castor series from Mike Carey, Dead Men’s Boots is about ghosts of criminals possessing humans to effectively allow them to live forever. I got about 2/3 the way through this book then left it on a plane and was stuck for a couple of weeks. As soon as I got home I bought another copy and continued.

I am now totally invested in Felix Castor. I’ve got two more books to read (and another due out at the end of the year) and I’m already starting to get separation anxiety at the thought of finishing the series. This is exactly how I felt about Harry Dresden when I was reading The Dresden Files.

Cheers

Tim…

Oracle Exadata Database Machine Handily Handles The Largest Database In Oracle IT. What Does That Really Mean?

In my recent post entitled Oracle Executives Underestimate SPARC SuperCluster I/O Capability–By More Than 90 Percent! I offered some critical thinking regarding the nonsensical performance claims attributed to the Sun SPARC SuperCluster T4 in one of the keynotes at Oracle Openworld 2011. In the comment thread of that post a reader asks:

All – has anyone measured the actual IOPS from disk as well as from flash in your Exadata (production) environment and compare with what the Oracle white paper or CXO presentations claimed?

What Have I Let Myself in For! – UKOUG this year

One of my favourite Oracle happenings of the year is fast approaching, the UK Oracle User Group technical conference {see/click on the link on the right margin}. I’ve blogged before ( like here, last year) why I think it is so good.

I try and present at the conference each year and I go no matter if I am presenting or not.

However, this year I think I might have got myself into trouble. I put forward 3 talks, expecting one or possibly two to get through. One on Index Organized Tables, one on IT disasters and one as an introduction to database design – I’ve moaned about it being a dying art so I figured I should get off my backside and do something positive about it. Each talk is in a different stream.

Good blogs to read

If you’re looking for more good Oracle blogs to read, here are two very good ones:
 

Matching the Expected Output – Analytic RANK, ROW_NUMBER, DENSE_RANK, or Something Different?

November 16, 2011 I noticed an interesting request on the comp.databases.oracle.misc usenet group, and I thought that I would make an attempt at solving the request.  The original poster (OP) stated that he had a table with data similar to the following: TX   ID   DEPT   LOCATION   LOAD 1    99    A        NY       12 2    99    A        [...]

UKOUG Agenda

As in previous years the UKOUG allows you to create a personalized agenda for the upcoming conference. To give you a flavour for some of the excellent presentations and to encourage you to register I’ve reproduced mine below, as with previous years this is a ideal wishlist, I’ll probably “die” halfway through various days and [...]

Configuring VNC Server on Fedora 16…

When Fedora 15 rocked up it brought with it a replacement for the old init-style startup called systemd. In Fedora 15, it was pretty easy to ignore this change as everything (including vncserver) ran pretty much the same as before.

Fedora 16 is a little more “aggressive” about it’s use of systemd. When you issue and old-style service command, you are in no doubt that things have changed.

[root@homer system]# service nfs stop
Redirecting to /bin/systemctl  stop nfs.service
[root@homer system]#

Once again, not a big deal in itself.

So that brings me to the reason for this post. The configuration of VNC Server has changed completely between Fedora 15 and Fedora 16. By default you can’t get away with editing the “/etc/sysconfig/vncservers” file anymore. That issue prompted me to knock up a quick article to remind myself how to do the systemd-style setup.

Why does the same job run slower on an exact clone?

A customer  was working with a clone copy of their production database for reports, but the cloned database reports were running slower than the same reports on production and they wanted to know why.

Ostensibly the machines were similar and the memory was the same, though it’s always worth verifying.  The first thing I checked was the load profile. If you have OEM you can look at the performance page and/or top activity page to see the load profile.  The load profile of production was much more CPU bound and much less I/O bound than the clone and their was clearly a difference.

The customer knew the time they the report was run on the clone  but was unsure exactly when it was run on production, though knew it had been run in the past day.

On the clone box, during the report run the load profile using SQL script to reproduce the performance graph looked like :

Star Transformation And Cardinality Estimates

If you want to make use of Oracle's cunning Star Transformation feature then you need to be aware of the fact that the star transformation logic - as the name implies - assumes that you are using a proper star schema.

Here is a nice example of what can happen if you attempt to use star transformation but your model obviously doesn't really correspond to what Oracle expects:

drop table d;

purge table d;

drop table t;

purge table t;

create table t
as
select
rownum as id
, mod(rownum, 100) + 1 as fk1
, 1000 + mod(rownum, 10) + 1 as fk2
, 2000 + mod(rownum, 100) + 1 as fk3
, rpad('x', 100) as filler
from
dual
connect by
level <= 1000000
;

exec dbms_stats.gather_table_stats(null, 't')

create bitmap index t_fk1 on t (fk1);

Profiling trace files with preprocessor external tables in 11g and some parallel execution hacking

If you work with SQL Trace files (and profile them) then you should check out the awesome novel use of the “external table preprocessor” feature explained by Adrian Billington here:

Ironically just a day after writing my “Evil things” article, I noticed a note in MOS about how to enable an event 10384 at level 16384 to get a parallel plan to be executed in serial: