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September 2014

Inmemory: Not all inmemory_size is usable to store tables.

I have been testing the inmemory column store product extensively and the product is performing well for our workload. However, I learnt a bit more about inmemory column store and I will be blogging a few them here. BTW, I will be talking about internals of inmemory in Oaktable world presentation, if you are in the open world 2014, you can come and see my talk:


Can you have high redundancy files in a normal redundancy diskgroup?

One of the perks of teaching classes is that I get to research questions asked. In the last Exadata Administration Class I taught someone asked: can you have your disk groups in Exadata on normal redundancy yet have certain databases use high redundancy? This would be a good interview question …

The answer is yes, which I remembered from researching material on the 11g RAC book but I wanted to prove that it is the case.

Update: I planned a second blog post where I wanted to test the effect but Alex Fatkulin was quicker, and I promise I didn’t see his post when I wrote mine. Otherwise there probably wouldn’t have been one :) In summary, you aren’t really any better protected. The disk group remains at normal redundancy, even with the data files in high. Looking at Alex’s results (and I encourage you to do so) I concur with his summary that although you have a 3rd copy of the extent protecting you from corruption, you don’t have higher resilience.

The primary election is over. Sadly, I did not win.

Either the power of social networking is not yet up to the task of overcoming television ads and the visual and other pollution of yard signs EVERYWHERE, or New Hampshire is not ready for the #SAFE_DEAL and to #IMPOVERISH_DRUG_LORDS. (Or, I suppose, they just didn’t like me. Quickly figuring my likely exposure, though, I believe a large percentage of folks who heard my message actually voted for me. So maybe I just need to get better and spreading the word at low cost. I do find it ironic that MAYDAY pac endorsed a candidate who did spend money on the grounds he pledged to fight against large campaign media budgets in the future, while I operated on a minimal media budget. Notice that is not a criticism of the candidate they did endorse.)

Anyway, completely cribbed from WMUR-TV’s site, here are the apparent 99% returns:

Brown, Scott 58,635    50%  Rubens, Jim   27,048 23%  Smith, Bob     26,483 23%

VirtualBox 4.3.16

virtualboxVirtualBox 4.3.16 has arrived. The downloads and changelog are in the usual places.

Although 4.3.14 worked fine on OS X and Linux, I skipped it on Windows because it just wouldn’t start a VM. That issue is allegedly fixed in this release. The changelog includes the following entry.

Windows hosts: fixed startup problems on certain Windows hosts due to conflicts with anti-virus software (4.3.14 regression, bug #13187)”

Happy days! :)



Oracle Midlands Event #5

Just a quick reminder. Oracle Midlands Event #5 is next Tuesday evening. Here is the information from the website.

I’ll see you there!



Oracle Midlands Event #5 was first posted on September 10, 2014 at 9:48 am.
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Intra-Database IORM in action

I have been teaching the Enkitec Exadata Administration Class this week and made an interesting observation I thought was worth sharing with regards to IO Resource Management on Exadata.

I have created a Database Resource Manager (DBRM) Plan that specifically puts a resource consumer group to a disadvantage. Actually, quite severely so but the following shouldn’t be a realistic example in the first place: I wanted to prove a point. Hang-on I hear you say: you created a DBRM plan-the post has IORM in the subject though: what gives? Please allow me to explain.

Exadata offers 3 different ways to implement IORM to the keen engineer:

Quiz Night

I have a table with several indexes on it, and I have two versions of a query that I might run against that table. Examine them carefully, then come up with some plausible reason why it’s possible (with no intervening DDL, DML, stats collection, parameter fiddling etc., etc., etc.) for the second form of the query to be inherently more efficient than the first.

Zone Maps On Commit Refresh Oddities

One of the ways Zone Maps can be refreshed when the underlying table data is changed is fast on commit. This is similar to how materialized views can be refreshed with the exception that a Zone Map does not need a materialized view log to do so.

It can also lead to some peculiar side effects.

Test setup

Let's begin by creating a test table with the on commit refresh materialized zone map:

SQL> create table t pctfree 95 clustering by linear order (n) as
2 select level n, rpad('x', 200, 'x') v
3 from dual
4 connect by level <= 5000;

Table created

SQL> create materialized zonemap zm$t refresh fast on commit on t (n);


SQL> select * from zm$t order by 1;

---------- ---------- ---------- ----------- ----------- ----------

Dear “Pro-life”: I am against abortion. But I am not against choice

If you run for office, you’ll get loaded questionnaires that essentially insist you sign up to overturn Roe v Wade. (And from the other side that you’ll sign up against things like the Hobby Lobby ruling, when the real issue is that individuals or families, not corporations, should control their own health care insurance choices.)

And let’s decode a little bit, since even the names of the movements are a lie: “Pro-life” means “I want to make abortion illegal.”

“Pro-choice” means I want the government to routinely fund abortion and make it a popular choice. I’m aligned with clinics that provide abortions and we tout the advantages to your life style of not having a child to raise or going through the inconvenience of carrying a child to term to be adopted.

ASSM Truncate.

Here’s one that started off with a tweet from Kevin Closson, heading towards a finish that shows some interesting effects when you truncate large objects that are using ASSM. To demonstrate the problem I’ve set up a tablespace using system allocation of extents and automatic segment space management (ASSM).  It’s the ASSM that causes the problem, but it requires a mixture of circumstances to create a little surprise.