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October 2012

count(*)

I came across a nice bit of code on OTN recently that someone had written several years ago (in 2007, in fact)  to demonstrate the different ways in which the optimizer would handle “select count({something}) from table;”. If you want to copy and repeat the test code, you may need to adjust it slightly – it references a type vc2s, which I changed to dbms_stats.chararray, and it references a plan table called toad_plan_table, which I replaced with references to the standard plan_table (getting rid of the truncate as I did so).

Adaptive Log File Sync: Oracle, Please Don’t Do That Again

Disclaimer: Much of what follows is pure speculation on my part. It could be completely wrong, and I’m putting it out there in the hopes that it’ll eventually be proven one way or the other.

Friday Philosophy – Is the CBO becoming way too complex?

I was at the SIOUG annual conference in Slovenia this week (and a very good conference it was too) and I was watching a presentation by Christian Antognini about how the CBO learns by it’s mistakes. This was of course mostly about adaptive cursor sharing and cardinality feedback. Chris was also able to share a few tid-bits about 12c enhancements in this area. I can’t go into details, but basically it looks like the CBO is going to not only enhance those two features but there is a new one where the CBO can change the plan on the fly, as the same query progresses.

Adaptive Log File Sync: Oracle, Please Don’t Do That Again

Disclaimer: much that follows is pure speculation on my part. It could be completely wrong and I’m putting it out there in the hopes that it’ll eventually be proven one way or the other.

Adaptive Log File Sync: Oracle, Please Don’t Do That Again

Disclaimer: much that follows is pure speculation on my part. It could be completely wrong and I’m putting it out there in the hopes that it’ll eventually be proven one way or the other.

VirtualBox 4.2.2 Released…

I knew there was something missing from my life. It seems ages since I’ve updated all my VirtualBox guest additions. :)

VirtualBox 4.2.2 is available, with the changelog and downloads in the usual place.

Happy upgrading.

Cheers

Tim…

How Many Children Can a Parent Cursor Have? 1,000,000?

The patch set 11.2.0.3 includes a fix for bug# 10187168 which, in reality, is an enhancement request. Its purpose is to artificially limit the number of child cursors that a parent cursor can have. The concept is quite easy: when a parent cursor reaches _cursor_obsolete_threshold (default value is 100) child cursors the parent cursor is obsoleted and, as a result, a new one is created.

So, as of 11.2.0.3 (or with some PSUs and bundle patches), the answer to the question is: 100.

OOW 2012 – The yearly AMIS Review from Oracle Open World and JavaOne

Yesterday (16th October), 10 days of the end of the yearly Oracle show in San Francisco, AMIS organized its ‘Review from Oracle Open World 2012′ session with an overview of news, trends, announcements, special finds and interesting rumors . This session was ‘sold out’ (even though it was free). For close to 4 hours, the …

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Philosophy 19

We’ve reached that time of year (Autumn, or Fall if you prefer the American term) when I’m reminded that tending a garden is like tending an Oracle database.

This is a picture of the oak tree on my front lawn, taken about 4 hours ago. Looking at it now it shows hardly any sign of the coming winter and little of the colour that let’s you know it’s preparing to drop its huge volume of leaves, but yesterday morning I spent the best part of an hour raking up leaves that had dropped over the course of the previous week.

Oracle exadata: pam and temporary user-lockout.

If you are administering an Oracle Exadata database machine, which base operating system image (the operating system version with which it system came) is Linux and version 11.2.3.1.0 (current version is viewable with the command ‘imageinfo’, which needs root account privileges) or higher, and multiple users are accessing the system with password authentication, this blogpost might be an interesting read. Also, if you have witnessed temporary lockout of the oracle user, or other users: this blogpost describes the reason and a potential resolution.