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December 2019

The 2019 Year in Review

It’s that time of year where everyone is doing a “Year in Review” post and why not?

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It’s good to gain perspective, plan for 2020 and celebrate all that was wonderful about 2019, (outside of politics, that was an utter failure on all fronts, pretty much most countries… :))

The DBAKevlar blog:

Oracle wait event ‘log file parallel write’ change

This post is about a change in how the time is measured for the event ‘log file parallel write’. This is important for the performance tuning of any change activity in an Oracle database, because with the default commit settings, a foreground session that commits changes waits in the wait event ‘log file sync’, which is a wait on logwriter activity, for which the wait event ‘log file parallel write’ always has been the indicator of the time spend on IO.

Log file sync
First things first: a foreground session normally waits on the wait event ‘log file sync’ when it commits waiting for its change vectors to be written to the online redologfile(s) by the logwriter. It is wrong to always assume a ‘log file sync’ will be present. If, somehow, the logwriter manages to increase the ON DISK SCN to or beyond the foreground session’s commit SCN, there will be no ‘log file sync’ wait event.

ADHD and Certification Tests- A Tale of Disaster

I don’t talk too much about my Attention Deficit Hyperactivity Disorder, (ADHD) brain outside of the occasional squirrel joke and more often view it as a super power, but when it is a challenge, I think it’s important to share what we go through.  You can’t solve a problem if you don’t know it is one.

ADHD and Autism

For those that aren’t aware, I was diagnosed with ADHD/on the spectrum for autism back in 2004-2005.  Its not that I wasn’t before this, I just grew up in a very rural area. I fully demonstrated traditional traits for a kid that suffered from both, just no one diagnosed me until one of my own children was diagnosed, (which is quite common.)  At that point in my life, I’d developed numerous, effective, coping mechanisms, but it still created enough challenges that I required medication to address some of the more serious symptoms.

Scalar Subq Bug

This is an observation that came up on the Oracle Developer Forum a couple of days ago, starting life as the fairly common problem:

I have a “select” that runs quickly  but when I use in a “create as select” it runs very slowly.

In many cases this simply means that the query was a distributed query and the plan changed because the driving site changed from the remote to the local server. There are a couple of other reasons, but distributed DML is the one most commonly seen.

In this example, though, the query was not a distributed query, it was a fully local query. There were three features to the query that were possibly suspect, though:

The Shepherd’s Crown


The Shepherd’s Crown is the last book in the Discworld series by Terry Pratchett. I really don’t like the finality of how that sounds, which is probably why I’ve waited a long time to read this book.

Friday Philosophy – Community Means So Much

There have been a few things in the last month that have really brought home to me how much I personally receive from the Community. In my case, my Community is primarily the Oracle User Community – The end users who come together to share knowledge, the Oracle employees who support this, and the companies that support the end users. For most of you reading this, you are part of the Oracle User Community, but most of you will be (I hope) in other communities too through your other interests, be they religious, music, hobbies, sports, charities etc.

Tools To Monitor and Work with Oracle on Azure

I’ve been studying for over a week for my certs.  It really is a challenge for my ADHD brain, as I learn by interacting and using a product, not be reading about it and guess what?  Most of what the certs are on are not in my technical area.  Yeah, this is not fun for me.  I find that my brain hits a limit on what it can absorb before the activity levels in the temporal lobes diminish and I need to take a break, which is what I’m doing right now after a full day of Azure Synapse Analytics, (yes, I know it’s not GA.  Yes, I know I have limited exposure to work with it, which means it’s going to be difficult for me to know at the deep level I’d need for a cert.  Yes, I want to find the person who added this, along with CosmosDB and Polybase as the main content for the cert… :))

Flashback Archive

A classic example of Oracle’s “mix and match” problem showed up on the Oracle Developer Forum a few days ago. Sometimes you see two features that are going to be really helpful in your application – and when you combine them something breaks. In this case it was the combination of Virtual Private Database (VPD/FGAC/RLS) and Flashback Data Archive (FDA/FBA) that resulted in the security predicate not being applied the way you would expect, hence allowing users to see data they were not supposed to see.

Philosophy – Treating Illness As A Performance Issue

Firstly, I’m on the mend. This is not a post about “oh woe is me, I am so ill”. But I have been rather ill.  I’ll just give you the highlights: The highs of UKOUG Techfest19 at the start of the month were followed very quickly by me developing full-blown influenza (Type A). After about 5 days of being ill in bed I realised I was fighting for breath just laying there. I analysed the problem and came to the conclusion “something else is very wrong and paracetamol is not the answer”. I was taken into hospital and put on increasingly powerful ventilating machines until they could get enough oxygen into me to keep me (sort of) functioning. I’d developed secondary infections & bronchitis, seriously reducing my lungs’ capacity to exchange oxygen & carbon dioxide.