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Logwriter I/O

If you are on any version of the database past 10.2.0.4, then savvy DBA’s may have noticed the following message popping up occasionally in their trace files


Warning: log write time 540ms, size 444KB

In itself, that is quite a nice little addition – an informational message letting you know that perhaps your log writer performance is worth closer investigation.  MOS Note 601316.1 talks a little more about this message.

So let’s say you have seen this warning, and you are interested in picking up more information.  Well… you could start scanning trace files from time to time, and parsing out the content etc, or do some analysis perhaps using Active Session History, but given that these warnings are (by default) triggered at above 500ms, there’s a chance you might miss them via ASH.

Extending Flashback Data Archive in 12c

Flashback Data Archive (previously called Total Recall) has been around for a long time now. For those unfamiliar with it, (and by the way, if you are on Enterprise Edition, you should be familiar with it, because its a free feature), here is a very quick primer.

Create a tablespace to hold your history, and create a flashback archive using that space allocation.

Hack-a-Mongo

I was reading an article today about how 10,000+ Mongo installations that are/were openly accessible on the internet have now been captured by ransomware, with nearly 100,000 other instances potentially vulnerable to the same issue.

Now, since I’m an Oracle blogger, you may be inclined to think the post is going to jump on the “bash MongoDB” bandwagon, but it’s not.  I am going to bash  something…but it’s not MongoDB Smile

AskTom takes another step forward

For over 16 years, AskTom has been one of the most valuable resources available to developers and database administrators working with the Oracle Database.  With over 20,000 questions tackled and answered, along with over 120,000 follow up’s to additional queries, it remains an outstanding knowledgebase of Oracle assistance.

And today, AskTom just got a whole lot better!

We’re excited to announce a new member of AskTom team…database evangelist Maria Colgan.  Many of you will know Maria for her work with Optimizer and In-Memory, but in fact she brings decades of expertise across the entire database technology stack to assist you with your questions. Maria blogs regularly at sqlmaria.com so make sure you check in there regularly as well. With Maria on the team, AskTom keeps getting better and better in 2017!

 

jmeter – Variable Name must not be null in JDBC Request

So Jmeter seems super cool.

I’ve only used it a little bit but it does seem a bit touchy about somethings (like spaces in input fields) and the errors are often less than obvious and I’m not finding that much out there on google for the errors.

Today I ran into the error

Variable Name must not be null in JDBC Request

 screen-shot-2017-01-06-at-12-01-10-pm

screen-shot-2017-01-06-at-12-00-50-pm

jmeter – getting started

jmeter

This blog post is just a start at documenting some of my experiences with jmeter. As far as load testing tools go, jmeter looks the most promising to me. It has an active community, supports many different databases and looks quite flexible as far as architecting different work loads goes.

The flexibility of jmeter also makes it hard to use. One can use jmeter for many other things besides databases so the initial set up is a bit oblique and there look to be many paths to similar results. As such, my understand and method for doing things will probably change considerably as I start to use jmeter more and more.

I’m installing it on a mac and using RDS instances.

installing jmeter

What you "liked" last year…

Well…when I say “liked”, what I mean is “the stuff you all clicked on a lot” last year. Whether you liked it or not will remain one of those great mysteries Smile

The top 6 posts from 2016 were:

https://connormcdonald.wordpress.com/2015/11/25/ora-14758-last-partition-cannot-be-dropped/

https://connormcdonald.wordpress.com/2013/01/20/exchange-partition-those-pesky-columns/

Graphics for SQL Optimization

Dan Tow, in his book SQL Tuning, lays out a simple method of tuning SQL queries. The method is

  • Draw a diagram of each table in the query with Children above Parents
  • Draw join lines between each join (many-to-many, one-to-many)
  • Mark each table with a predicate filter and calculate the amount of table filtered out

Then to find a great optimal optimization path candidate

  1. Start at the table with the strongest predicate filter (the filter that returns the fewest % of the table)
  2. join down to children (if multiple children join to child with strongest predicate filter)
  3. If you can’t join to children, join up to parent

The basics are pretty simple and powerful. Of course there are many cases that get more complex and Dan goes into these complex cases in his book.

When local partitions….aren’t

Let’s say I’ve got a partitioned table, and because New Year’s eve is coming around, I certainly don’t want to be called out at 12:01am because I forgot to add the required partition for the upcoming year Smile.

Since 11g, I can sleep easy at night by using the INTERVAL partition scheme. Here’s my table

UKOUG 2016

Just a little video montage of the fun and learning from UKOUG.  A great conference every year.