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June 2012

OUGN Conference 2012

I'm going to kick off this post by really blowing my own trumpet! There have been times (perhaps not many) when I've heard that posts here have influenced others and helped them make decisions. That always catches me by surprise (erm, I suppose I should stop being surprised by now), but it's brilliant too. One example is that I've met several people who first considered working for Pythian because my blog post about their interview process stuck in their minds. Of course, people like Paul Vallee and Alex Gorbachev are master recruiters, too, but I did my bit in some cases.

The new lab server has arrived

Update: the Oracle Linux memory problem is solved: http://martincarstenbach.wordpress.com/2012/06/13/kernel-uek2-on-oracle-linux-6-2-fixed-lab-server-memory-loss/

As part of an on-going research project I have invested a little bit of money towards a new lab server. Sadly my Phenom II X6 with 16GB RAM was not on the HCL for ESXi 5 which I required. Before I knew that ESXi can itself be virtualised I looked at a number of options.

After much consideration and calculations I decided to buy a machine. I have already rented a Core i7-2600 with 32GB of RAM from Hetzner (which is superb value for money for their EX4-check it out!) but needed something more flexible in terms of OS installation and virtualisation. Although the team at Hetzner is most helpful and skilled, installing ESXi or Oracle VM 3.1.x would have been quite a task. Especially hardening the setup!

Truncate Partition

A recent posting on the OTN database forum (which I didn’t answer correctly on my first attempt) raised the problem of truncating partitions when there are referential integrity constraints in place. Let’s start with a demonstration of the problem:

Fedora 17 : My upgrade hell…

It’s been a few days since the final release of Fedora 17. I’ve been running it on VMs since the alpha release, but the day after the final release I decided to upgrade a real Fedora 16 machine. That’s where all the fun started…

I’ve now attempted Fedora 16 -> 17 upgrades on two physical servers and both have been destroyed by the process. In both cases, I had to do a fresh install, which worked cleanly and left a fully functioning installation. Perhaps I’m just very unlucky, but with a record of 0 for 2, my conclusion is that the upgrade process on Fedora 17 sucks so much ass it’s untrue.

As followers of the blog know, I try to keep my host machines pretty clean and do anything of significance in VirtualBox VMs. As a result, the recovery of both systems has been fine, if a little slow. In both cases, I did a clean install, then copied back all the VMs and that was pretty much it.

Subpartition stats

You might have expected the following query ought to run reasonably efficiently, after all it seems to be targeted very accurately at precisely the few rows of information I’m interested in:

select
	column_name,
	avg_col_len
from
	dba_subpart_col_statistics
where
	owner             = 'TEST_USER'
and 	table_name        = 'TEST_COMP'
and	subpartition_name = 'P_MAX_D'

I’m after some subpartition column stats (so that I can work out whether a subpartition of a local index on a composite partition is roughly the right size) and I’m querying the view by the only columns that seem to be there to allow me to access the data efficiently. Unfortunately the execution plan isn’t doing what I need it to do. The following plan is coming from a small 11.2.0.3 database with up to date statistics:

SLOB Is Not An Unrealistic Platform Performance Measurement Tool – Part II. If It’s Different It’s Not The Same.

In Part I of this series I discussed the concept of “Mindless I/O” and contrasted Orion I/O testing to SLOB.

Some time has passed since that post and a lot of folks have been studying their systems using SLOB. Others have been motivated to prove that the differences between SLOB and Orion are moot. I’m OK with that because I use both of them and a large array of other I/O tools (fio, bonnie, etc,etc).

Test Single Block Random Reads With SLOB And Call It A Day
There is something I’d like to quickly point out about SLOB.

My return to the rat race…

I mentioned on Twitter recently that I’d started a new job, which was greeted with some amusement. Some of my friends in the Oracle community have spent the last 4 years ribbing me about being “unemployed”. For those that don’t know the story, I was never unemployed. I am an employee of my own company, which paid me for the last 4 years. I spent that time representing the Oracle ACE Director program at conferences around the world, doing some teaching for Oracle University, but most of the time was spent at home, on my computers playing with Oracle technology , writing about it and answering questions about it. I had no serious intention of joining the rat race again in the foreseeable future, but at the same time I would never say never…

Advertorial: upcoming appearances

I’ve got a few speaking commitments in the next few months, which might be of interest to you:

Planboard DBA Symposium

This conference is held in Utrecht, NL on the 12th of June. Some of the speakers include: Alex Nuijten and Rob van Wijk. I’ll be presenting about multiblock reads, and try to explain some of the differences which where silently introduced with Oracle version 11.

Prometheus…

Let me start by saying, I’m a big fan of all the Alien films, even Alien 3, which seems to be the least liked. Having said that, if someone said I had to pick one it would always be Alien. I watch that film several times a month. :)  Ridley Scott is renowned for being uncompromising, so I went into Prometheus with some seriously high expectations, which always worries me as it kinda sets you up for a fall…

The opening sequence of Prometheus is quite possibly the most beautiful thing I’ve ever seen on film. As I watched it I thought it was probably worth the £6 just to see that on a big screen…

Reverse Path Filtering and RAC

This is a quick note about reverse path filtering and impact of that feature to RAC. I encountered an interesting problem recently with a client and it is worth blogging about it, with a strong hope that it might help one of you in the future.

Problem

Environment is 11.2.0.2 GI, Linux 5.6. In a 3 node cluster, Grid Infrastructure (GI) comes up cleanly in just one node, but never comes up in other nodes. If we shutdown GI in first node, we can start the GI in second node with no issues. Meaning, GI can be up in just one node at any time.

System Admins indicated that there are no major changes, only few bug fixes. Seemingly, problem started after those bug fixes. But there were few other changes to the environment /init.ora parameter change etc. So, the problem was not immediately attributable to just OS changes.


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