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Making sense of direct path reads during primary key lookups

I recently made an interesting observation while monitoring database performance on an Oracle Enterprise Edition system. While looking at some ASH data (for which you must be licensed appropriately!) I came across direct path reads attributed to a select statement performing a primary key lookup. At first, this didn’t make much sense to me, but it’s actually intended behaviour and not a bug.

In this post I’m reproducing what I observed. I am using Oracle 18.4.0 for this experiment running on my Linux lab environment. The hardware uses 1s8c16t with 64 GB of memory.

Little things worth knowing: the latest public-yum-ol7.repo configuration file enables an upgrade to UEK R5

For a little while now I have been using Ansible for all installation/configuration tasks I do in the lab. I can’t really be bothered to do these things by typing commands anymore: once you get the hang of Ansible, you can develop an urge to automate everything. As part of my playbook installing the Oracle database on Oracle Linux, I replace /etc/yum.repos.d/public-yum-ol7.repo with the current version from Oracle’s server to make sure I have the latest and greatest software available.

Linux grub2 boot loader manipulation

This post is about how to manage grub2 in an easy way.


In the past, which is before linux EL7, the boot loader was grub, the grand unified bootloader (version 1). Things were very simple; if you installed another kernel (using rpm) it would add an entry to grub’s configuration in /boot/grub/menu.lst. If you wanted to change grub to boot that newly installed kernel by default you edit /boot/grub/menu.lst and set ‘default’ to the number, counting from zero, of the newly installed kernel, in the order of the kernels listed. If you wanted a certain option set for booting the kernel, you added it to the kernel line.

Little things worth knowing: parallel Data Pump export in table mode

I haven’t used Data Pump in a little while but recently needed to do a bit of work involving this very useful utility to export a single table. I know that it is possible to export data in parallel using expdp, but I can’t recall the syntax for doing so off the top of my head when I need it. This post describes a potential approach to exporting a table in parallel. In the next post I will demonstrate an interesting case where using parallelism didn’t help me speed up the export. All of this was tested on 12.2 and 18.4.0, the examples I am sharing originate from my 18.4.0 single instance database (without ASM) running on Linux.

The setup

My lab environment is a bit limited when it comes to storage, so I’ll have to do with small-ish tables. The basic principles should still apply for larger segments though. Please note that my tables aren’t partitioned to keep the individual segment size as large as possible. 

Installing Ansible on Oracle Linux 7 for test and development use

There are a few alternative ways of installing Ansible on Linux, and the install guide for Ansible 2.7 (the current version at the time of writing) does a great job in explaining them all in detail.  There is a potentially easier way to get to a current Ansible version if you are using Oracle Linux 7, but it comes with a very important limitation. Let’s get that out of the way first.

OBUG Tech Days Belgium 2019 – Antwerp – 7/8-FEB-2019


Dates: February 7 and 8, 2019

Location: in Antwerp, Belgium

More information soon.

For people from the netherlands: this is easy reachable by car or by train! This is a chance to attend a conference and meet up with a lot of well-known speakers in the Oracle database area without too extensive travelling.

Bootstrapping a VM image in Oracle Cloud Infrastructure using cloud-init

At the time of writing Oracle’s Cloud Infrastructure as a Service (IaaS) offers 2 ways to connect block storage to virtual machines: paravirtualised and via iSCSI. There are important differences between the two so please read the documentation to understand all the implications. I need all the performance I can get with my systems so I’m going with iSCSI.

Enhanced “validate” commands in Oracle’s Data Guard Broker 18c

If you are using an Oracle Database Enterprise Edition chances are that there is at least one environment in your estate making use of Data Guard. And if you are using Data Guard, why not use the broker? I have been using Data Guard broker for a long time now, and it has definitely improved a lot over the first releases, back in the day. I like it so much these days that I feel hard done by if I can’t make use of it. This is of course a matter of personal preference, and I might be exaggerating a little :)

One of the nice additions to the broker in Oracle 12.1 was the ability to validate a database before a role change. This is documented in the Data Guard broker documentation. I certainly don’t solely rely on the output of the command, I have my own checks I’m running that go over and above what a validate can do.

Log in to Ubuntu VMs in Oracle Cloud Infrastructure

When I learned that Oracle was providing Ubuntu images in Oracle Cloud Infrastructure (OCI) I was a bit surprised at first. After all, Oracle provides a great Enterprise Linux distribution in the form of Oracle Linux. As a Ubuntu fan I do of course appreciate the addition of Ubuntu to the list of supported distributions. In fact it doesn’t end there, have a look at the complete list of Oracle provided images to see what’s available.

Trying Ubuntu LTS

I wanted to give Ubuntu a spin on OCI and decided to start a small VM using the 16.04 LTS image. I have been using this release quite heavily in the past and have yet to make the transition to 18.04. Starting the 16.04 VM up was easily done using my terraform script. Immediately after the terraform prompt returned I faced a slight issue: I couldn’t log in:

Terraforming the Oracle Cloud: choosing and using an image family

For a few times now I have presented about “cloud deployments done the cloud way”, sharing lessons learned in the changing world I find myself in. It’s a lot of fun and so far I have been far too busy to blog about things I learned by trial and error. Working with Terraform turned out to be a very good source for blog posts, I’ll put a few of these up in the hope of saving you a few minutes.

This blog post is all about creating Ubuntu images in Oracle Cloud Infrastructure (OCI) using terraform. The technique is equally applicable for other Linux image types though. In case you find this post later using a search engine, here is some version information that might put everything into context: