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March 2018

Result cache invalidation caused by DML locks

In a previous post about Result Cache, I was using ‘set autotrace on’ in my session to see when the result cache hit saves the logical reads. I got a comment, by e-mail and with full test case, mentioning that the invalidation I had when doing some DML does not occur when autotrace is set to off. I reproduced the problem, on 18c because I use my cloud services to do my tests, but it works the same way in 12c.

I’ll focus here on DML which does not modify any rows from the table the result depends on, because this is the case that depends on the session transaction context. When rows are modified, the result is always invalidated.

Friday Philosophy – Not My Cup Of Tea

A few days ago I tweeted a copy of a “motivational poster”. I don’t normally like motivational posters but this one struck a chord with me as it was a lesson I took a long time to learn. Not everyone will be your cup of tea. Which is a very British (I think) way of saying you don’t like something or someone. “Ohh, that Mavis, she’s just not my cup of tea!”.

GDPR Solutions in the Day of Automation

There’s something for having job security and many of the solutions that I see offered for RDBMS challenges offer just that. With compliance with EU’s GDPR, (General Data Protection Regulations) just around the corner, (mark you calendar, May 25, 2018) you’d think we’d all be scrambling for a simpler solution to discovering and addressing all that GDPR data.

Quick refresher for those of you going, “What is GDPR?”

Data security is a known focus of GDPR when you talk to folks, but it’s much more than just security.  It’s about extended rights of the individual in the EU. There’s four areas as a DBA, you need to really concern yourself with:

Video demo of installing RANDOM_NINJA

First video in a longer series on how to install, use and extend RANDOM_NINJA. This one, is a quick
one simply showing how to install the package.

Video demo of installing RANDOM_NINJA

First video in a longer series on how to install, use and extend RANDOM_NINJA. This one, is a quick
one simply showing how to install the package.

Keeping Intervals

I’ve recently been reminded of a blog post I wrote a couple of years ago that discussed the issue of running into the hard limit of 2^20 -1 as the number of segments for a (composite) partitioned table – a problem that could arise in a relatively short time if you used a large number of hash subpartitions in an interval/hash composite partitioned table (you get about 2 years and 10 months of daily partitions at 1,024 subpartitions per day, for example).

No Asynchronous I/O When Using Shared Server (Also Known As MTS)

I've recently had a case at a client where it was questioned why a particular application was seemingly not making full use of the available I/O capabilities - in comparison to other databases / applications using similar storage.

Basically it ended up in a kind of finger pointing between the application vendor and the IT DBA / storage admins, one side saying that the infrastructure used offers insufficient I/O capabilities (since the most important application tasks where dominated by I/O waits in the database), and the other side saying that the application doesn't make use of the I/O capabilities offered - compared to other databases / applications that showed a significantly higher IOPS rate and/or I/O throughput using the same kind of storage.

Text indexes for numbers

We had an AskTOM question recently about being able to search for numbers within a concatenated list. The particular issue was a list of mobile phone numbers, but this is really just about tackling the larger issue of finding numbers within list.

Let’s create a simple example to see where things can break down (and how we can fix them).

Linux timing and scheduling granularity

During investigating how Oracle works with regards to waiting, I discovered an oddity. I was researching for my redo blog posts, and found that in a certain case, Oracle uses the ‘nanosleep’ system call. As the name of this system call suggests, this call allows you to let a process sleep with nanosecond precision.

The oddity that I found, was the following:

Deferred Invalidation

I was going to write an article on the way 12.2 has introduced the option for “deferred invalidation” for a number of DDL operations, but I did a quick google search before I started writing and found that both Franck Pachot and Richard Foote (yes, rebuild index is one of the operations) had got there long ago, so here are a couple of links – as much for my own benefit as anything else:

Richard Foote:

Franck Pachot: