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December 2012

Hash Join Buffered


Introduction

A few years ago Jonathan Lewis published a blog post that described one of the interesting side effects of Oracle's Parallel Execution implementation: Sometimes operations that usually are non-blocking will be turned into blocking ones.

Dune…

I’ve been a fan of the film Dune for ages. I also liked the TV mini series. The Children of Dune TV mini series was a bit too random for me. A remake of Dune is in the offing. With that in mind it is a little surprising to me that I’ve never got round to reading the book until now.

I think it’s safe to say I loved it. It’s one of the coolest things I’ve read in ages. Watching the film and TV series did not spoil it for me in the slightest, and quite unusually, reading the book has not lessened my love of the film.

Update Error

When doing updates with statements that use correlated subqueries, it’s important to make sure that your brackets (parentheses) are in the right place. Here are two statements that look fairly similar but have remarkably different results – and sometimes people don’t realise how different the statements are:

update t1
set
        padding = (
                select
                        t2.padding
                from    t2
                where   t2.id = t1.id
        )
where   t1.small_vc <= lpad(20,10,'0')
;

update t1
set
        padding = (
                select
                        t2.padding
                from    t2
                where   t2.id = t1.id
                and     t1.small_vc <= lpad(20,10,'0')
        )
;

DBMS_XPLAN.DISPLAY_CURSOR And Parallel Execution


Introduction

DBMS_XPLAN.DISPLAY_CURSOR can be used to get more insights into the actual resource consumption on execution plan operation level when using the GATHER_PLAN_STATISTICS hint (from 10g on), or increasing the STATISTICS_LEVEL parameter to ALL (on session level, on system level the overhead is probably prohibitive).As soon as a SQL execution is done (either successfully, cancelled or with error) the corresponding extended data in the child cursor gets populated/updated and the additional information about the actual runtime profile can be accessed via V$SQL_PLAN_STATISTICS resp.

Sharing a Kindle account

I have discovered that sharing a Kindle account with family members can cause Amazon to prompt me with the oddest reading suggestions:

Oaktable Sunday 2012

 
Abstracts
 
8-bit Oak Roots
Bernie Dugggs, Imagine Software

There’s a reason so many Oakies are about the same age. We were the keen users of the first popular computers. The British version of that experience was based on cheap and available 8-bit home computers that unleashed people’s latent passion, talent and ingenuity in over-coming platform limitations.
Bernie Dugggs will take a nostalgic look at his personal history as a developer of commercial ZX Spectrum computer games for Imagine, Ocean and Odin and show how relevant the experiences and lessons learned have remained throughout a career in software

 
 

Friday Philosophy: It’s Not What you Know – It’s What you are Getting To Know.

This has been a good but tiring week. It started with the UKOUG TEBS conference where I saw lots of people I know, a few who I didn’t but now do and I had good times in pubs and restaurants. One evening culminated in my singing part of “Two out of Three ain’t bad” in the style of a munchkin with Nial Litchfield in a pub at 1am, which I am sure he woud rather forget about – so if you know him, ask him about it. For me that was the indicator to go lie down in the dark and sleep. Irrespectve of drunken singing, I must had talked about 20 topics with 40 people over the conference, exchanging ideas, tricks and war stories.

Adding disks to VMware Workstation 8 on the fly on RHEL 6

Although this post is primarily written for users of VMware Workstation 8 it is applicable for any RedHat 6 clone and adding disks with single path on the fly. Multipathing requires additional setup in dm-multipath or the vendor multipathing software which I won’t cover here. A quick hint though: you need to set disk.EnableUUID = “TRUE” in your VM’s config file for scsi_id to return a value.

The situation is common: you created a virtual machine and need more storage. Hopefully you created it using LVM which would allow you to add the new disk to an existing volume group followed by a resize operation of the logical volume which is short on space. But before you can do this you have to add a new LUN to your setup-here is how you can do this without rebooting the VM.

First I recommend you install lsscsi (for convenience, not really necessary) and the sg3_utils:

UKOUG 2012

The UKOUG 2012 conference was a rather short affair for me this year as I was only there for 1 day of it.

During the Sunday I was at my nephew’s birthday party. In the evening I returned to Birmingham in time to make it to the Oracle ACE dinner. Big thanks to Debra Lilley for organizing it and to the Oracle ACE program for sponsoring the event. I used the opportunity to ask a number of questions about ADF and WebLogic. I’m still a newbie and since I seem unable to distance myself from the subject, I figured I need to know a bit more. :)

Monday was my first and only day at the conference. The lineup was like this:

UKOUG day 3

Today’s task – chairing the Unconference from 9:00 to 15:00 (though the first slot hasn’t been booked by anyone and, at this stage, I don’t think it will be).

Here’s the current agenda: