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Oracle multi-tenant and library cache isolation

This post is the result of a question that I got after presenting a session about Oracle database mutexes organised by ITOUG, as a response to the conference cancellations because of COVID-19. Thank Gianni Ceresa for asking me!

The library cache provides shared cursors and execution plans. Because they are shared, sessions can take advantage of the work of previous sessions of creating these. However, by having these shared, access needs to be regulated not to have sessions overwrite each other’s work. This is done by mutexes.

The question I got was (this is a paraphrased from my memory): ‘when using pluggable databases, could a session in one pluggable database influence performance of a session in another pluggable database’?

The Oracle ACE Program : My 14 Year Anniversary

I was checking my calendar, thinking I was about to jack it in for the day, and I noticed it’s April 1st, which means it’s my 14th year anniversary of being an Oracle ACE. Can’t believe I nearly missed that!

As usual I’ll mention some of the other anniversaries that will happen throughout this year.

World Backup Day- Backing up an Oracle Database using RMAN to Azure Blob Storage

A DBA is only as good as their last backup…or more so, their last recovery.

To celebrate #WorldBackupDay on Twitter, I’m blogging on how to backup an Oracle database directly to Azure Blob storage.  Yes, you could backup on a managed disk directly connected to the VM, then copy it off, but Azure Blob Storage is inexpensive and provides considerable speed and opportunity to create an NSF mount to use the backups with other Oracle hosts for cloning, recovery, etc.

Configure Blob Storage in the Azure Portal

In this example, we have an Oracle database running on an Azure IaaS VM and need to backup the database with RMAN.  No RMAN repository catalog will be used, but yes, you can use one-  no problem.

If you don’t already have a database and want to play along, you can perform the following blog post to create one.

Create a Simple Oracle VM on Azure IaaS

Use the following shell script to create your Oracle VM.  I chose the following parameters to create mine:

Using Azure Cloud Shell and with persistent storage, which are linked on the github page, I uploaded the mk_oravm.sh script and run it after changing the permissions.

chmod 744 mk_oravm.sh

Provision the VM

Run the script:

 ./mk_oravm.sh

Anwser the questions from the script:

Oracle recovery concepts

I’ve published a while ago a twitter thead on some Oracle recovery concepts. For those who are not following twitter, I’m putting the whole thread here:
 

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Locating Oracle Enterprise Linux Images for Azure

Just like with other UI’s, the Azure portal may not show you the wealth of offerings that can be found in the Azure catalog.  For those Oracle DBAs hoping to build an IaaS VM image from a certified OS version, this means they need Oracle Enterprise Linux and are frustrated when they can’t locate it in the portal.

Empower with the Cloud Shell

Oracle DBAs rarely are fascinated with user interfaces or portals, so when you offer us something like the Azure Cloud Shell, it’s something we should embrace.  I’ve spoke about it before and I will rave about it again here.  If you haven’t set it up, skip the download to your desktop and simply go to Azure Cloud Shell and connect to your Azure account.  Once there, ensure you’ve set the CLI to BASH and use this just as you would Putty or Xterminal.

Oracle disables your multitenant option when you run on EC2

I have installed Oracle 19.6 on an EC2 for our Multitenant Workshop training. And of course, during the workshop we create a lot of PDBs. If you don’t have paid for the Enterprise Edition plus the Multitenant Option you can create at most 3 pluggable database. But with this option you can create up to 252 pluggable databases. Does it worth the price, which according to the public price list is USD 47,500 + 17,500 per processor, which means per-core because Oracle doesn’t count the core factor when your Intel processors are in AWS Cloud (according to the Authorized Cloud Environments paper)?

Video : Online Segment Shrink for Tables : Free Unused Space

In today’s video we’ll give a demonstration of how to shrink tables that contain a lot of free space. As I say in the video, this is not something you should do regularly. It’s only necessary if you’ve done some drastic one-off maintenance, like a large data purge maybe.

There are a few articles this relates to.

ANSI hinting

I’ve made casual remarks in the past about how “ANSI”-style SQL introduces extra complications in labelling or identifying query blocks – which means it’s harder to hint correctly. This is a note to show how the optimizer first transforms “ANSI” SQL into “Oracle” syntax. I’m going to write a simple 4-table join in classic Oracle form and check the execution plan with its query block names and fully qualified table aliases; then I’ll translate to the ANSI equivalent and repeat the check for query block names and aliases , finally I’ll rewrite the query in classic Oracle syntax that reproduces the query block names and fully qualified table aliases that we got from the ANSI form.

We start by creating and indexing 4 tables (with a script that I’ve been using for various tests for several years, but the results I’ll show come from 19c):

Oracle rowcache fastgets

This blogpost is about the Oracle database row or dictionary cache. This is a separate cache that caches database metadata, like database object properties or user properties.

There is surprising little in-depth technical detail about the row cache. To some degree I understand: issues with the row cache are rare.

I noticed a column in V$ROWCACHE called ‘FASTGETS’. Whatever FASTGETS means, in my database it is being used: