LittleArduinoProjects#174 USB LED Notifiers

So four of these USB Webmail Notifier devices turned up in a dusty cupboard
in the office.

A quick tear-down shows they contain a super-simple circuit - just a
SONiX Technology SN8P2203SB 8-Bit microcontroller that handles the USB protocol and drives an RGB LED. The SN8P2203SB is an old chip phased out 2010/04/30, superseded by the SN8P2240. They have a supremely primitive USB implementation - basically mimicking a very basic USB 1.0 HID device.


The Oracle wait interface granularity of measurement

The intention of this blogpost is to show the Oracle wait time granularity and the Oracle database time measurement granularity. One of the reasons for doing this, is the Oracle database switched from using the function gettimeofday() up to version 11.2 to clock_gettime() to measure time.

This switch is understandable, as gettimeofday() is a best guess of the kernel of the wall clock time, while clock_gettime(CLOCK_MONOTONIC,…) is an monotonic increasing timer, which means it (more...)

Checksum entire directory using md5sum

When you are backing up 3.5+ TB database, resulting in 600+ GB backupset, transferring to new DC, you would want to ensure there are no corruptions resulting from transfer.

Here is an example of how to perform checkum using md5sum for all the contents in the directory.

Taking the process further, split the .md5 file into multiple files for parallel processing.

$ md5sum *MIG* > backup.md5

$ cat backup.md5
080adb9ba716f3bf6f91efb06adc311e   (more...)

PL/SQL context switch, part 2

This is the second blogpost on using PL/SQL inside SQL. If you landed on this page and have not read the first part, click this link and read that first. I gotten some reactions on the first article, of which one was: how does this look like with ‘pragma udf’ in the function?

Pragma udf is a way to speed up using PL/SQL functions in (user defined function), starting from version 12. If you want (more...)

Linux Perf Probes for Oracle Tracing

Topic: this post is about Linux perf and uprobes for tracing and profiling Oracle workloads for advanced troubleshooting.


The recent progress and maturity of some of the Linux dynamic tracing tools has raised interest in applying these techniques to Oracle troubleshooting and performance investigations. See Brendan Gregg's web pages for summary and future developments on dynamic traces for Linux. Some recent work on applying these tools and techniques to Oracle can be found (more...)

PL/SQL context switch

Whenever you use PL/SQL in SQL statements, the Oracle engine needs to switch from doing SQL to doing PL/SQL, and switch back after it is done. Generally, this is called a “context switch”. This is an example of that:

-- A function that uses PL/SQL 
create or replace function add_one( value number ) return number is
        l_value number(10):= value;
        return l_value+1;
-- A SQL statement that uses the PL/SQL function
select sum(add_one(id))  (more...)

Introducing stapflame, extended stack profiling using systemtap, perf and flame graphs

There’s been a lot of work in the area of profiling. One of the things I have recently fallen in love with is Brendan Gregg’s flamegraphs. I work mainly on Linux, which means I use perf for generating stack traces. Luca Canali put a lot of effort in generating extended stack profiling methods, including kernel (only) stack traces and CPU state, reading the wait interface via direct SGA reading and kernel stack traces and getting (more...)

Oracle 12 and latches, part 3

This post is about manually calling and freeing a shared latch. Credits should go to Andrey Nikolaev, who has this covered in his presentation which was presented at UKOUG Tech 15. I am very sorry to see I did miss it.

Essentially, if you follow my Oracle 12 and shared latches part 2 blogpost, which is about shared latches, I showed how to get a shared latch:

SQL> oradebug setmypid
Statement processed.
SQL> oradebug  (more...)

Fedora LAMP Steps

I posted earlier in the year how to configure a Fedora instance to test PHP code on a local VM. However, I’ve got a few questions on how to find those posts. Here’s a consolidation with links on those steps:

  1. Go to this blog post and install the httpd and php libraries with the yum installer.
  2. In the same blog post as step 1 (you can put the sample PHP code into the /var/www/html directory (more...)

RAM is the new disk – and how to measure its performance – Part 3 – CPU Instructions & Cycles

If you haven’t read the previous parts of this series yet, here are the links: [ Part 1 | Part 2 ].

A Refresher

In the first part of this series I said that RAM access is the slow component of a modern in-memory database engine and for performance you’d want to reduce RAM access as much as possible. Reduced memory traffic thanks to the new columnar data formats is the most important enabler for the awesome In-Memory processing (more...)

My New Youtube Channel

I have created a new youtube channel – and have uploaded some videos there already! Bookmark & Subscribe here:

More stuff is coming over the next weeks & months :-)


NB! After a 1.5 year break, this year’s only Advanced Oracle Troubleshooting training class (updated with Oracle 12c content) takes place on 16-20 November & 14-18 December 2015, so sign up now if you plan to attend this year!

Linux Kernel Stack Profiling and Flame Graphs Applied to Oracle Investigations

Topic: This blog post is about kernel stack profiling and visualization with flame graphs with examples.

Stack profiling and flame graphs are very useful techniques and tools for troubleshooting and investigating workloads at the OS-level and understand which code path take most of the execution time. You can find extensive material and examples o flame graphs in Brendan Gregg's website and blog. A few additional examples of using stack tracing and flame graphs for (more...)

Little things worth knowing: automatic generation of extended statistics in 12c

When you are migrating to Oracle 12c I hope you might this post useful. I came across this feature when researching what’s new with Oracle 12c (and yes I still find lots of new ones I haven’t noticed before). This one is a bit hidden away in section Automatic Column Group Detection of the 12c New Features Guide. And it’s a lot more complex than I first thought! In this first post (more...)

How the log writer and foreground processes work together on commit.

(warning: this is a rather detailed technical post on the internal working of the Oracle database’s commit interactions between the committing foreground processes and the log writer)

After the Trivadis Performance days I was chatting to Jonathan Lewis. I presented my Profiling the log writer and database writer presentation, in which I state the foreground (user/server) process looks at the commit SCN in order to determine if its logbuffer contents are written to disk by (more...)

OEL/RHEL 7 – firewalld

How cool is getting Linux. Hope soon to not look like a Windows. If they put a butterfly or shiny window in the “start menu” I’m out of the game. The “new” firewalld is cool and dynamic, but my servers are square, boring and static. Maybe if I’m using RHEL/OEL 7 in my laptop it […]

SLES shell script to check required os packages according to documentation before starting oracle forms & reports installation


If you try to install oracle forms & reports on SLES 11.3 than despite all installer checks are passed maybe you get a message like:

Error in invoking target ‘install’ of makefile ‘<FR_HOME>/sqlplus/lib/’.

The reuirement check of the installer shows only missing openmotif classes which are not really required on SLES (see Doc ID 1567715.1), but no problems with a compiler or something similar.

Checking for binutils-2.19-11. (more...)

Web Pages Not Databases – Part 2: Fail2ban, Apache, IP Addresses, Linux, SELinux

August 23, 2015 (Back to the Previous Article in this Series) I started using Linux in 1999, specifically Red Hat Linux 6.0, and I recall upgrading to Red Hat Linux 6.1 after downloading the files over a 56k modem – the good old days.  I was a little more wise when I upgraded to another […]

Installing the Oracle database in docker

This blogpost is about how to install and run the Oracle database in docker. Please mind this is not an officially supported virtualisation platform for the Oracle database. This is a proof of concept setup.

Linux host setup.
In my setup, I used a linux host, freshly installed with Oracle Linux 6.7, which is going to be used as docker server. Please mind you need to leave diskspace (or a disk device) unused for (more...)

Preparing a Oracle Linux for a Vagrant box

This post is an overview of an installation and configuration process of the Oracle Linux, which will be used as a machine “box” for Vagrant software using a Virtual Box platform.

Post itself is divided into two parts:

  1. Oracle Linux installation (points 1 to 12)
  2. Vagrant box configuration (points 13 to 16)

Part 1 – Oracle Linux installation


1. Create a new Virtual Machine - machine name will be used later to create Vagrant (more...)

CloneDB in Oracle

I personally really like CloneDB, a way to thin-clone an Oracle database over NFS. This can be quite interesting, and I wanted to update my blog for (April PSU). Tim Hall has a good example for and later, and I covered cloneDB it in the Consolidation Book in some detail as well.

My setup is as follows:

  • server3 (Oracle Linux 7.1) uses Oracle Restart and has (more...)