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Showing posts from December, 2015

A few thoughts about OCM 12c upgrade

Yesterday I sat for the 12c OCM upgrade exam, which I mentioned in few blog posts before. The first step after checking your ID is of course signing the NDA, and thus you won't find much real information here.

This time I chose Utrecht as the place to take the exam. Not that I have any special preference, I took each of the exams in a different place so far. The only requirements were convenient time and location defined as 'somewhere in Europe'. But in the end, Utrecht turned out to be a good place. Oracle NL headquarters are easy accessible, it's a very new building, the lunch was good:-)
And the city is nice to see.

Regarding the exam, the usual important notes still hold true:

Arrive on time. It's a long day and you will have a lot of things to do.You will work hard the whole day. Get a good sleep before, be well rested.Review the exam topics well. Note that they may have change over time. There is for example an update as of January 1, 2016: Flex ASM was added…

Don't trust the lying (Data Guard) broker

One of the new 12c features is the "VALIDATE DATABASE" command. According to the documentation it should do many thorough checks and tell you if all is configured well and correctly. However, there is one catch - or to put it a little more bluntly - bug. Or two.

You know that you need standby redo logs for SYNC (or the new FASTSYNC) transport mode. The validate command knows that, too. And you know that you should have one more standby redo log than online redo logs. The validate command seems to know this one as well.

However, the checks appear to have one flaw: they test whether the threads (and let's talk here about a single-instance, so we have only thread #1) have enough standby redo logs (SRLs) assigned. But when you create an SRL with 'alter database add standby logfile', they are unassigned to any thread. In fact, you get 0 as thread#:

select thread#, sequence# from V$STANDBY_LOG; THREAD# SEQUENCE# ------- --------- 0 0 0 0 …

UKOUG Tech15 is over, looking forward to Tech16

What a busy week! The UKOUG Tech15 conference made me busy for four days, postponing any other work and non work stuff.
As usual, I met many people actually using our products - it's always a bit strange feeling and a strong confirmation seeing people trusting their data and apps to something a developer writes:-)
And of course, seeing many old friends again was also very nice. Especially talking to Gluent guys (http://gluent.com) and seeing what they are up to was very interesting and promising - I hope they succeed in a big way and change the data landscape.

And of course, the Twinkies...

Oracle transactions in the new world

If the new world of BigData, NoSQL and streaming has sparked your interest, you may have noticed one peculiarity - the lack of proper transactions in these contexts (or transactions at all!) Yes, durability is retained, but the other properties of ACID (Atomicity, Consistency, Isolation, Durability) leave a lot to be desired.

One might think that in this new world perhaps applications are built in such a way that they no longer need it,  and in some cases this may be true. For example, if a tweet or an update to Facebook gets lost, then who cares, and we can simply continue on. But there is of course more important data that still requires transaction support and some NoSQL databases have limited support for this nowadays. However, this is still far from a full implementation, the likes of which everyone takes for granted in the Oracle database (e.g. you cannot modify just arbitrary rows in arbitrary tables in a single transaction). Of course, the huge benefit is that these databases …