Calling all Oracle Tasmanians :-)

I’m in Hobart Tasmania for a half day on Monday (Feb 29).  If you’re in town, please drop in and say Hi – should be a fun morning

Here is the agenda

09:00 – 09:15 am General introduction

09:15 – 10:15 am Presentation – Diary of an 11.2 upgrade

10:15 – 10:30 am Morning tea

10:30 – 11:30 am Presentation – Optimizer stats strategies – a fresh approach

11:30 – 12:30 pm Presentation – Miscellaneous SQL features

12:30 – 01:30 pm Lunch, general questions and networking

Morning tea and a  light lunch will be provided so it would be very much appreciated if you could RSVP so we can correctly cater for the event by email to president.tas@ausoug.org.au

 

See you there !

MOS–the brave new world

Its been a long hard painful road….

But finally, we no longer have to ensure that Flash-based mistake that was unleased onto the world a few years back Smile

I freely admit that I’ve been a scathing critic of the MOS flash interface, both on newsgroups and internally via feedback to the support team themselves, and to be honest, I thought that this would all be falling on deaf ears.

So I’m happy to say that somewhere inside the organisation, people were obviously listening to myself (and the many others), because we finally have an interface that looks promising and at first usage, seems functional and practical.

UKOUG–feedback from attendees

Just a short note to say thank you to anyone that took the time to score, rate and comment on my presentations at the UKOUG this year.  Whether you loved my talks, or hated my talks, I’m always flattered by anyone that takes the time to give the feedback that all speakers desire in order to better cater toward the preferences of the attendees at conferences.  After all, its the attendees that are paying the money – they deserve the best that we can give.

Updating primary keys and triggers

I recently came across an example where someone wanted to update primary keys with an INSTEAD-OF trigger (on a view). It can be done, but I wanted to demonstrate that you need to take extreme care, because you can get some problems you might not have forseen.

If you choose to allow primary key updates, then you’ve pretty much got two options:

1) “simple update”

The incoming SQL is say:



        update ...

        set   col7 = :new.col7

        where ...

and the instead-of trigger takes a “global” approach, ie, all columns



        update ...

        set   pk = :new.pk,

              col1 = :new.col1,

              col2 = :new.col2

        where ...

where the column list includes the primary keys…

The problem here is that even an update of a primary to the same value, is still an update to the primary key – which means increased locking for any child tables. It means a pretty careful review of any foreign keys, and associated foreign key indexes.

2) “conditional update”

The instead-of trigger checks to see if the PK columns are being altered, and only includes them if appropriate



 if :old.pk != :new.pk then
          update ...
          set   pk = :new.pk,
                col1 = :new.col1,
                col2 = :new.col2
          where ...
        else
          update ...
          set   col1 = :new.col1,
                col2 = :new.col2
          where ...
        end if;

Still challenges here – because a set operation has now become a row-by-row operation….Consider the following example:



SQL> create table T ( x number primary key, y date );

Table created.

SQL> insert into T values (1,sysdate);

1 row created.

SQL> insert into T values (2,sysdate);

1 row created.

SQL> insert into T values (3,sysdate);

1 row created.

SQL> insert into T values (4,sysdate);

1 row created.

SQL> create or replace

  2  view V as select * from T;

View created.

SQL> create or replace
  2  trigger TRIG instead of update on V
  3  for each row
  4  begin
  5    update T
  6    set x = :new.x
  7    where x = :old.x;
  8  end;
  9  /
Trigger created.

That all seems straightforward enough – but now we’ll compare updates on the base table and view…


SQL> update T set x = x + 1;

4 rows updated.

SQL> roll;

Rollback complete.

No problems there – each primary key was incremented by 1, and then oracle ensured statement level integrity, ie, no duplicates

Now lets try the exact same operation on our view


SQL> update V set x = x + 1;

update V set x = x + 1
       *
ERROR at line 1:
ORA-00001: unique constraint (SYS_C00177683) violated
ORA-06512: at "TRIG", line 2
ORA-04088: error during execution of trigger TRIG'

Uh oh….ker splat !

That’s actually a best case scenario – because at least the thing crashed. Things can get really gnarly once you start doing primary key updates across tables. For example:



SQL> create table PARENT ( p number primary key );

Table created.

SQL> create table CHILD ( f_p number constraint FK references PARENT );

Table created.

SQL> insert into PARENT values (1);

1 row created.

SQL> insert into PARENT values (2);

1 row created.

SQL> insert into PARENT values (3);

1 row created.

SQL> insert into CHILD  values (1);

1 row created.

SQL> insert into CHILD  values (2);

1 row created.

SQL> insert into CHILD  values (3);

1 row created.

SQL> create or replace
  2  trigger TRIG after update on PARENT
  3  for each row
  4  begin
  5    update CHILD set f_p = :new.p where f_p = :old.p;
  6  end;
  7  /

Trigger created.

SQL> UPDATE PARENT SET p = p+1;

3 rows updated.

SQL> select * from parent;

         P
----------
         2
         3
         4

SQL> select * from child;

       F_P

----------
         4
         4
         4

Nothing crashed – but we totally corrupted the child table. This last example is actually also contained in the standard Oracle docs.

And you also have to really ask the question – who or what is updating a primary key ? That’s just a bad idea, triggers or not.

UKOUG day 3

Today was a bumper day for content.

Day 3 started with Doug Burns taking the p*ss out my presentation style…The cheek of the man ! Smile  All in good fun, although Doug is such a sensitive soul, the temptation to mess with him and claim offense was very very high.  He gave a great talk on statistics on partitioned objects, which was very relevant given my client’s recent embarkation on a new data warehouse.

Then I ran back and forth between presentations on indexes and memory – its a tough call when you want to see two presenters, but you also dont want to be one of those rude people that leaves halfway through.  I opted for the “sneak out when presenter turns their back” option, and seemed to get away with it.

Harald van Breederrode (http://prutser.wordpress.com/) gave a great talk on smart flash cache in Oracle.  Unfortunately we are AIX, so its of limited use for us currently, but still a cool piece of technology.  For those who don’t know, he’s legally blind, but still knows more about Oracle than just about anyone on the planet…astounding.

My final talk for the conference was on Optimizer stats, which is really a light hearted way of telling people to take more care and more time with their stats, and they’ll be amazed at the benefits they will get.  I did this talk on Sunday as well – in front of optimizer boss Maria Colgan – so hopefully any of my gentle digs at the optimizer were well received.  Of course, if not, then tough…I’ll always be a ranter Smile

And that was about the size of it….next stop was Birmingham airport, and then a glorious 20 hours on a plane back to Perth.

If anyone cannot locate the slides for my talks, please drop me a line and I’lll send you them.

UKOUG day 2

Firstly, I hope everyone had a great Christmas…I took a few weeks off in December which explains the blog hiatus…but back to the grind stone now Smile

Well, day 2 started much like day 1….4am the internal body clock told me to get up, and thus I did some work on my slides, and then promptly fell back to sleep and missed the first session on the morning.

I went to Alex’s (http://nuijten.blogspot.com/) presentation on Analytics, a personal favourite topic of mine, since I’ve done talks myself on it, and I always like seeing someone else’s take on it.  I also liked the clean format of his slides – in fact, one of the cool things I’ve seen at all conferences around the world in the past year, is the abandonment of “corporate templates” in favour of the just high quality content.  I’d like to think I’ve had a small influence in that, but I like the trend.

Next up was my own talk on the saga of upgrades I had in 2011.  Its a funny talk to give, because there’s not a lot of technical content but because of the stress and pain those upgrades had, I still get a physiological response when I’m doing the talk – I get sweaty and adrenalin – all memories of a time when we nearly lost millions of dollars with a down system.  But the talk went well and I felt like a rock star because my ugly mug was on the big screen behind the stage Smile

I was pretty much spent after that – I tried to catch John B’s talk on ASH and Jonathan Lewis’s talk on the optimizer, but as I felt myself falling to sleep in each, I had to give up and head back to the hotel for a sleep.  A hour of recovery sleep, and I was back Luca’s talk on storage options at CERN and Ray Wang’s keynote.

Then it was off to the masquerade ball.  I bombed out about 11pm, but apparently many Oakies partied hard into the night!

UKOUG day 1

Well, as per normal when attending a conference in another country, it started very early….very early indeed.  4am the body clock decided it was time to get up, so eventually just gave up on trying to get back to sleep and started the day Smile

First up was Kyle Hailey’s talk on SQL Tuning.  Kyle is very passionate about his stuff, and his Visual SQL Tuning is all about graphing rather than “reading” the execution plan.  He was in Hall 1, which this year is projecting the speaker up on the big screen next to the slides…Should be fun for my talk in that room tomorrow !

Next up was my partitioning talk, which went OK, although its one of those talks that just bludgeons people with streams and streams of content and examples. So by the end of the 60 minutes, you can tell when people are “full” and can’t take much more Smile

One thing that’s interesting this year is the size of the exhibition hall.  There seems to be a lot less exhibitors here – I wonder if they this is a reflection of the fact that generally conferences seem to be attracting technical people rather than middle management.  (And technical people don’t have an operating budget, so the exhibitors are not seeing it as a worthwhile investment…who knows).

Here’s a picture of the hall in case anyone hasn’t seen how these things are mapped out:

 

P1050418

 

The afternoon sessions included Julian Dyke and Martin Bach’s talk about clusterware upgrades – both of which tend to mirror the content I’ll be doing tomorrow, namely …. its painful.

(Day 2 and Day 3 will be coming in a couple of weeks….I’m off to Rottnest (http://www.rottnestisland.com/) for a couple of weeks – no laptop, no internet…