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August 2018

RV Life and Working Remote

I get a lot of questions about what it’s like to work remote while living in our 5th wheel.  I’ll link this post to, too, so for those asking the same question from that site, it’s a two for one… </p />

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Descending bug

Following on from Monday’s posting about reading execution plans and related information, I noticed a question on the ODC database forum asking about the difference between “in ({list of values})” and a list of “column = {constant}” predicates connected by OR. The answer to the question is that there’s essentially no difference as you would be able to see from the predicate section of an execution plan:

Take care with regular expressions

In an Office Hours session a couple of months back, I covered an important change that comes to regular expressions once you upgrade to 12c Release 2. You can see the video covering the issue here:

but for the TL;DR brigade reading this post: Regular expressions are not deterministic when you take NLS settings into account and thus cannot be used in constraints and/or function-based indexes.

This is just a post to quickly revisit the topic for anyone thinking of upgrading from an earlier release to 12c Release 2. An AskTOM question came in asking what would happen to such constraints during the upgrade process.

Parallel Execution of PL/SQL

A recent experience with text searching showed up some limitations on parallel execution of PL/SQL functions, and how to work around them.

Gooey GUIDs

Do a quick Google search and you’ll find plenty of blog posts about why GUIDs are superior to integers for a unique identifier, and of course, an equal number of posts about why integers are superior to GUIDs. In the Oracle world, most people have been using sequence numbers since they were pretty much the only option available to us in earlier versions. But developers coming from other platforms often prefer GUIDs simply due to their familiarity with them.

A tribute to Natural Join

By Franck Pachot

I know that lot of people are against the ANSI join syntax in Oracle. And this goes beyond the limits when talking about NATURAL JOIN. But I like them and use them quite often.

Masterclass – 1

A recent thread on the Oracle developer community database forum raised a fairly typical question with a little twist. The basic question is “why is this (very simple) query slow on one system when it’s much faster on another?” The little twist was that the original posting told use that “Streams Replication” was in place to replicate the data between the two systems.

Installing ZFS on OEL7 UEK4

Here are the commands I use to setup ZFS on Oracle Linux

#This was tested on OEL 7.2 in Oracle Cloud Compute Classic and OEL 7.5 in Oracle Cloud infrastructure
set -x
cat /etc/oracle-release
yum -y install kernel-uek-devel-$(uname -r)
yum install -y yum-utils
yum-config-manager --enable ol7_developer_EPEL
yum install -y dkms
rpm -Uvh
sudo yum install -y zfs
dkms status
/sbin/modprobe zfs
systemctl -a | grep zfs
echo "ZFS Pool creation on the last disk added:"
zpool create -f myzpool -m /mnt/myzpool /dev/$(lsblk | awk 'END{print $1}')
zpool status
zpool list

The full blog is on:

Installing ZFS on OEL7 UEK4 for Docker storage - Blog dbi services

MySQL 5.6 vs 5.7

Whitelist preview of Performance Insights has just started on RDS MySQL and it gave me a chance to visually compare load profiles of MySQL 5.6 and 5.7.

I first tried to use sysbench and ran into some curious anomolies.

The test I ran was

sysbench \
           --test=oltp \
           --oltp-table-size=10000000 \
           --oltp-test-mode=complex \
           --num-threads=10 \
           --max-time=0 \
           --max-requests=0 \
           --mysql-host=$host \
           --mysql-user=$user \
           --mysql-password=$password \
           --mysql-db=sysbench run

Load chart on MySQL 5.6 and 5.7


MySQL 5.6

I first ran on MySQL 5.6 and in Performance Insights the load looked like:

Automatic Table Reorganization in #Exasol

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