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February 2012

Subquery Factoring

Here’s an interesting little conundrum about subquery factoring that hasn’t changed in the recent ( patch for subquery factoring. It came to me from Jared Still (a fellow member of Oak Table Network) shortly after I’d made some comments about the patch. It’s an example based on the scott/tiger schema – which I’ve extracted from the script $ORACLE_HOME/rdbms/admin/utlsampl.sql (though the relevant scripts may be demobld.sql or scott.sql, depending on version).

As usual I’ve used an 8KB block size, LMT with uniform 1MB extents, and no ASSM to hold the data. I won’t reproduce the code to generate the schema, just the versions of the query with, then without, subquery factoring:

Temporary tablespaces in RAC

Temporary tablespaces are shared objects and they are associated to an user or whole database (using default temporary tablespace). So, in RAC, temporary tablespaces are shared between the instances. Many temporary tablespaces can be created in a database, but all of those temporary tablespaces are shared between the instances. Hence, temporary tablespaces must be allocated in shared storage or ASM. We will explore the space allocation in temporary tablespace in RAC, in this blog entry.

In contrast, UNDO tablespaces are owned by an instance and all transactions from that instance is exclusively allocated in that UNDO tablespace. Remember that other instances can read blocks from remote undo tablespace, and so, undo tablespaces also must be allocated from shared storage or ASM.

Space allocation in TEMP tablespace

Next Public Appearance – Scottish SIG on 29th Feb

Who’s up for a beer or whiskey in Edinburgh on the evening of 28th Feb?

I’ve been promising myself I’d do the Scottish SIG for three or four years but life has always conspired to stop me. However, at last I am going to manage it this year.

The meeting is on the 29th February at the Oracle {was Sun} office in Linlithgow. You can see the schedule and details here. As ever, it is being chaired by Thomas Presslie, though I {and I suspect Mr Hasler} will be hoping he is not forcing drams of Whiskey on people before 10am in the morning, as he did at the last UKOUG conference…

Tuning is in the eye of the beholder… Memory is memory right?

It is human nature to draw from experiences to make sense of our surroundings.  This holds true in life and performance tuning.   A veteran systems administrator will typically tune a system different from an Oracle DBA.  This is fine, but often what is obvious to one, is not to the other.  It is sometimes necessary to take a step back to tune from another perspective.

I recently have ran across a few cases where a customer was tuning “Sorts” in the database by adding memory. Regardless of your prospective, every one knows memory is faster than disk; and the goal of any good tuner is to use as much in memory as possible.   So, when it was noticed by the systems administrator that the “TEMP” disks for Oracle were doing a tremendous amount of IO,  the answer was obvious right?

Will Enabling a 10046 Trace Make My Query Slower (or Faster)?

February 13, 2012 (Modified February 14, 2012) It seems that I often wonder about the things that I read… is it really true?  Several years ago, one of the items that I wondered about is whether or not an execution plan for a SQL statement could change magically simply because the Oracle RDBMS knows that it is [...]

Oracle Security Training in Berlin ... and more ...

I am going to be teaching by two day Oracle security training course in Berlin on March 6th and 7th 2012 for DOAG - the German Oracle users group. You can find details of the course and also register to....[Read More]

Posted by Pete On 13/02/12 At 11:57 AM

RMOUG 2012 training days

In the next few days I’ll be at RMOUG 2012 training days! and I’ll be again presenting the topic so dear to my heart. Mining the AWR </p />

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How Many Non-Exadata RAC Licenses Do You Need To Match Exadata Performance?

This post is about exaggeration.

The Oracle Database running in the Database Grid of an Exadata Database Machine is the same as what you can run on any Linux x64 server. Depending on the workload (OLTP/ERP/DW.BI.Analytics) there is the variable of storage offload processing freeing up some cycles on the RAC grid when running Exadata. Yes, that is true.

We all know the only thing that really costs Oracle IT shops is Oracle’s licensing and Oracle’s license model is per-processor.

So the big question is whether spending a significant amount of money for Exadata storage actually reduces the Oracle Database licensing cost due to offload processing. Or, in other words, does the magic of Exadata offload processing save you money.

SQLTXPLAIN quick tips and tricks and DB Optimizer VST

Lately I’ve been busy on projects and research so I’m putting more and more stuff on my wiki/braindump… and really I need to catch up on blogging.
I have a longer draft post about SQLTXPLAIN.. but I haven’t finished it yet so I’ll just go with the quick post for now.


I’ve been using SQLTXPLAIN for quite a while, and I can say I’m a really big fan. It’s a cool tool to use for systematic SQL Tuning so I got them all neatly documented here

The 10th Annual Hotsos Symposium is coming...

I remember the first Hotsos Symposium like it was yesterday.  It was a time I got to meet many people I had interacted with online for the first time - like Jonathan Lewis for example.  I cannot believe it was 10 years ago...

I've attended all but one of these events over the years (and I definitely won't be missing the 10 year anniversary!) - it is one of the few conferences where I try to attend as many sessions as I can myself.  One thing I like is there are only two tracks at most - meaning you'll miss some content you probably wanted to see - but nothing on the scale of the larger conferences out there with 10, 20 or more concurrent tracks.

The party they throw every year isn't bad either.  (the food is probably the best conference food ever ;) )