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Oracle

LAOTN Tour (Southern Leg) Preparation Complete…

Tomorrow is going to be a very tough day. I’ve got work as normal, including one of my fortnightly Tuesday presentations. From work I dash home, get changed, pick up my stuff and it’s off to the airport. I get a quick flight to Paris, then it’s a 14.5 hour flight to Santiago, Chile. That’s the starting point for the southern leg of the LAOTN tour this year. I can only hope I break the habit of a lifetime and actually get some sleep on the plane. If not I’m going to be like Day of the Dead when I get there.

Oracle Certified Professional (OCP) Database 12c…

I just noticed the Database 12c OCP beta exams have started to appear (see here).

Not surprisingly, the multitenant option seems to be a big factor in the content of the both the Advanced Administration and Upgrade exam.

There are a few things that see a little odd (to me) though:

Temporary undo

Back in Oracle 8i the Global Temporary Table was introduced to reduce the overhead of storing temporary data inside the database. A Global Temporary Table stores its data in a Temporary Tablespace where the data is retained for the duration of either a single transaction or the lifetime of a session. Performing DML on a […]

Oracle Database File System (DBFS) Enhancements in Oracle 12c

Oracle 12c includes a really neat feature I first mentioned after Oracle OpenWorld 2012. You can now access your DBFS file systems over HTTP/HTTPS, FTP or WebDAV. I’ve been having a play with it over the last couple of days, so I thought I would write it up here.

This should be quite a welcome addition for those people on platforms other than Linux, who don’t get to use FUSE.

As mentioned in the article, WebDAV support under Windows 7 broken. Even the Oracle manual has a screen shot from Windows XP. I can’t believe Windows 7 has been out all this time and Microsoft have not bothered to fix it…

Cheers

Clustering_factor

The clustering_factor is one of the most important numbers (if not the most important number) affecting the optimizer’s choice of execution plan – it’s the thing that has the most significant effect on the optimizer’s decision on whether to choose a table scan or an index, and on which index to choose.

Keyword DETERMINISTIC is anything but…

According TheFreeDictionary.com, the word “deterministic” means…

deterministic
de·termin·istic adj. an inevitable consequence of antecedent sufficient causes

According to Wikipedia, the explanation of deterministic algorithm is…

Analyzing IO at the Exadata Cell level… iostat summary

While analyzing Write-Back cache activity on Exadata storage cells, I wanted something to interactively monitor IO while I was running various tests.  The problem is summarizing the results from ALL storage cell.  So, I decided to use my old friend “iostat” and a quick easy script to roll up the results for both DISK and FLASH.  This allowed me to monitor the IOPS, IO size, wait times, and service times.  

The “iostat-all.sh” tool shows the following data:

Parallel to Serial

Here’s a little problem that came up on the Oracle-L listserver today:

I’m trying to write a query which reads the corresponding partition of the fact, extracts the list of join keys, materialises this result set, and finally joins the necessary dimensions. The key thing I’m trying to do is to run the initial query on the fact in parallel and then the rest of the query serially.

Upgrading to Oracle Database 12c : First Steps…

I’ve taken my first tentative steps into upgrading to Oracle 12c.

This article is targeted at the type of information you are likely to need for the 12c OCP DBA exam. In reality, upgrades are too important to rely on a generic article like this. Every time I do a real upgrade I go back to the upgrade docs and work my way through them. That’s the only way to make sure you’ve not missed out an important step, specific to the features you are using.

My first impressions are:

Linear Decay

I’ve mentioned “linear decay” in several posts when explaining a problem that someone has seen with an execution path – but I’ve recently realised that I don’t have a post describing what it is and how it works – although it’s in Cost Based Oracle – Fundamentals, of course, if you want some detail – so here’s a brief introduction (based on simple stats with no histograms).