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May 2018

AMM vs security

Most of us already know that AMM sucks. But usually, we think about disadvantages of AMM in terms of performance. Let’s see why it sucks in the terms of security </p />
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Bitmap Join Indexes

I’ve been prompted by a recent question on the ODC database forum to revisit a note I wrote nearly five years ago about bitmap join indexes and their failure to help with join cardinalities. At the time I made a couple of unsupported claims and suggestions without supplying any justification or proof. Today’s article finally fills that gap.

VMWare Experts Program, Sydney

A few weeks back, I received an invitation from Don Sullivan to attend the Sydney version of the VMWare Experts Program. I worked with Don during our time at Oracle, and caught up with him again a couple of years ago at one of the Collaborate conferences. He had moved on to VMWare, and is still working for them today.

Partition-Wise Operations – New Features in 12c and 18c

Partition-wise operations are not something new. I do not remember when they were introduced, but at that time the release number was still a single digit. Anyway, the aim of this post is not to describe the basics, but only to describe what is new in that area in 12c and 18c.

The new features can be grouped in three categories:

  • Partition-wise GROUP BY enhancements available as of version 12.2
  • Partition-wise DISTINCT enhancements available as of version 12.2
  • Partition-wise windowing functions enhancements available as of version 18.1

Before looking at the new features, here are the SQL statements I executed to create a partitioned table that I use through the examples. You can download the script here.

12c upuserxt.lst, upobjxt.lst & Oracle Maintained objects/users

Mike Dietrich has blogged recently about upuserxt.lst and upobjxt.lst and how to query them with external table. The first time I’ve seen those ‘.lst’ files, the default extension for sqlplus spool files, I wondered whether they were provided in ?/rdbms/admin on purpose, or if they were just some leftovers from some tests Oracle did before packaging the Oracle Home. Finally, I realized that they were there on purpose and that those ‘.lst’ are important files when upgrading to 12c.

Time for #GLOC, #SQLSatDallas, #DataSummit18

The next nine days, I’m traveling to three cities for four events. We’ll just call this the 9-3-4 gauntlet of speaker life. I booked this travel as four, one-way flights to get the itinerary
I needed to make the most of my schedule and will have breaks between each event to make sure I don’t kill myself my last two weeks at Delphix.

GLOC

Getting started with #Exasol

One nice and easy way to make yourself familiar with Exasol – the leading In-Memory Analytic Database – is the Community Edition. It’s free and can be downloaded here as a virtual machine running on VirtualBox.

A good description how to install the Community Edition can be found here.

There’s an Exasol SQL Client called EXAplus. You can use it as GUI, then it looks like this:

ADWC – connect from your premises

In the previous post about the Autonomous Data Warehouse Service, I’ve run queries though the Machine Learning Notebooks. But you obviously want to connect to it from your premises, with SQL*Net.

CaptureADWCconnect001Of course the connection, going through the public internet, must be secured. If you already use a managed service like the Oracle Exadata Express Cloud Service, you already know how to do: download a .zip containing the connection string and the wallet and certificate for SQL*Net encryption.

From file names to directory hierarchy

I had a fun request come in from a colleague the other day.  They had a simple list of fully qualified file names and they needed to present that data in the familiar hierarchical tree layout. 

To demonstrate, I took a little trip down memory lane Smile and grabbed a subset of presentations I’ve done over the years.

Skip Scan 3

If you’ve come across any references to the “index skip scan” operation for execution plans you’ve probably got some idea that this can appear when the number of distinct values for the first column (or columns – since you can skip multiple columns) is small. If so, what do you make of this demonstration: