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September 2019

Nologging

Bobby Durrett recently published a note about estimating the volume of non-logged blocks written by an instance with the aim of getting some idea of the extra redo that would be generated if a database were switched to “force logging”.

Since my most recent blog notes have included various extracts and summaries from the symbolic dumps of redo logs it occurred to me that another strategy for generating the same information would be to dump the redo generated by Oracle when it wanted to log some information about non-logged blocks. This may sound like a contradiction, of course, but it’s the difference between data and meta-data: if Oracle wants to write data blocks to disc without logging their contents it needs to write a note into the redo log saying “there is no log of the contents of these blocks”.

Dead Connection Detection (DCD) and the Oracle database

Dead Connection Detection is a useful feature of the Oracle database: it allows for the cleanup of “dead” sessions so they don’t linger around consuming memory and other system resources. The idea is simple: if the database detects that a client process is no longer connected to its server process, it cleans up. This can happen in many ways, in most cases this kind of problem is triggered by an end user.

A dead connection shouldn’t be confused with idle connections: an idle connection still maintains the network link between client and server process, except that there is no activity. Idle connections aren’t maintained/controlled via DCD, there are other tools in the database handling such cases.

As a by product, DCD can also help with overly eager firewalls forcibly removing seemingly idle network connections. I found the following posts and the references therein very useful:

UKOUG 2019

At the UKOUG TechFest 2019 event in Brighton this year I’ll be chairing the CBO Panel session on Monday 2nd December at noon. The panellists will be Maria Colgan, Nigel Bayliss, Christian Antognini and Richard Foote.

It will be possible to propose questions on the day – written or spoken, but this if you have a question that you’d like to give the panellists a little warning about then you can:

Installing an #Exasol 2+0 Cluster on Hyper-V

After having installed Hyper-V, an ISO file with the Exasol software needs to be downloaded. The 2+0 cluster consisting of two data nodes and one license server needs a host machine with at least 8 GB memory and 60 GB free disk space. I do it on my Windows 10 notebook with 16 GB memory. This is for educational purposes of course and not suitable for production use.

2+0 means two active nodes and no reserve node. A reserve node can be added later, expanding the environment to a 2+1 cluster.

We’ll start adding two virtual switches to be able to connect the network adapter of the VMs to them later.

Create Hyper-V Switches for Private and Public Network of the cluster

Click the Virtual Switch Manager in Hyper-V Manager:

Presenting at UKOUG Techfest19 Conference in Brighton, UK

I’m very excited to be attending my 3rd UKOUG Conference, this year re-badged as Techfest19. The fact it’s being held in Brighton is a little disconcerting for a Crystal Palace fan, but really looking forward nonetheless to what has always been one of the very best Oracle conferences on the yearly calendar. I have a […]

19c High-Frequency statistics gathering and Real-Time Statistics

Those are the two exciting new features about the optimizer statistics which arrived in the latest release of 12cR2: 19c. Less exciting is that we are not allowed to use them in any other platform than Exadata:

https://apex.oracle.com/database-features/

But let’s cross the fingers and hope that this will be released in the future because they solve real-life problems such as Out-of-Range queries. Here is a little example involving both of them. A table starts empty and is growing during the day. Relying only on the statistics gathered during the maintenance window will give bad estimations. And dynamic sampling may not sample the right blocks.

Join us in a Digital Climate Strike

With fires raging in the Amazon, hurricanes ripping across the Atlantic, and typhoons flooding Japan, our planet and our climate are sending us a message: We can no longer continue with business as usual.

The week starting September 20th, 350.org is organizing a Global Climate Strike, in association with Fridays For Future, to show global leaders that the time to act is now. Alongside the people walking out of workplaces, schools, and homes around the world, 350.org is organizing a digital climate strike. Websites participating in the digital strike will promote the physical strikes in the lead-up to the date, and partially block themselves to users on September 20th itself. That is where you come in!

Announcement: Australia/NZ “Let’s Talk Database” Events October 2019 !!

I’ve very excited to announce the next series of Oracle “Let’s Talk Database” events to be run throughout Australia and New Zealand in October 2019. I’ll be discussing two exciting topics this series, “Oracle Database 19c New Features” and “Oracle Exadata X8“. As always, these sessions run between 9am-1pm, include a networking lunch and are free, […]

WordPress.com and Fiverr Partner to Launch “WordPress.com Fundamentals” Course

Getting your new business website ready for launch? Want a little hand-holding — a step-by-step tutorial on setting up a WordPress.com site from start to finish, that you can work on at your own pace and on your own time? “WordPress.com Fundamentals,” a comprehensive video course created with our friends over at Fiverr, walks you through all the fundamentals in 90 minutes.

The course covers the basics of setting up a business website, but anyone new to WordPress.com can benefit from lessons on how to create an account, set up a site, customize a theme, publish content, and share it on social media. It was developed by WordPress.com Happiness Engineers with years of experience guiding thousands of new WordPress.com customers in chat, email, forums, and concierge sessions, so you know you’re getting expert guidance from people who know every WordPress.com tip and trick.

Oracle Database 19c Automatic Indexing: Default Index Column Order Part II (Future Legend)

In Part I, we explored some options that Oracle might adopt when ordering the columns within an Automatic Index by default, in the absence of other factors where there is only the one SQL statement to be concerned with. A point worth making is that if all columns of an index are specified within SQL […]