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August 2010

Filter “Bug”

Here’s an example to remind you how important it is to look at the “Predicate Information” supplied with an execution plan. Here are two execution plans that look very similar in shape – a continuous set of steps inwards and downwards from parent to child, with no “multi-child” parent rows:


--------------------------------------------------------------------------
| Id  | Operation                      | Name    | Rows  | Bytes | Cost  |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |         |     1 |    19 |     4 |
|   1 |  TABLE ACCESS BY INDEX ROWID   | MIN_MAX |     1 |    19 |     2 |
|*  2 |   INDEX UNIQUE SCAN            | MM_PK   |     1 |       |     1 |
|   3 |    SORT AGGREGATE              |         |     1 |     8 |       |
|   4 |     FIRST ROW                  |         |    10 |    80 |     2 |
|*  5 |      INDEX RANGE SCAN (MIN/MAX)| MM_PK   |    10 |    80 |     2 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("MM1"."ID_PARENT"=100 AND "MM1"."ID_CHILD"= (SELECT
MAX("MM2"."ID_CHILD") FROM "MIN_MAX" "MM2" WHERE "MM2"."ID_PARENT"=100))
5 - access("MM2"."ID_PARENT"=100)

And then this:

Some Blog Errors Are Just Too Serious To Ignore. A Comparison of Intel Xeon 5400 (Harpertown) to Intel Xeon 5500 (Nehalem EP).

I’d like to direct readers to an important blog update/correction. In my post entitled An Intel Xeon 5400 System That Outperforms An Intel 5500 (Nehalem EP) System? Believe It…Or Know It I blogged about an erroneous conclusion I had drawn about a test performed on these two processor models. I think the update does the blog [...]

OOW 2010 Plans and Anti-plans

I have plenty of things that are keeping me busy for OOW 2010 and you’ll all get to see the results at the event (if you’re there), but I only have one traditional technical session where I’ll be on stage. I’m presenting the following session jointly with an Oracle Database Machine customer:

Session ID: S316824
Title: Top 10 Lessons Learned in Deploying the Oracle Exadata
Tuesday, September 21, 12:30PM
Location: Moscone South, Rm 307

Check the OOW 2010 content catalog for updated room assignments and times.

What can EHCC do for you?

What can EHCC do for you?
By now you have probably heard about ExaData Hybrid Columnar Compression (EHCC), but what benefit can EHCC give you in terms of storage and performance savings?  
 
As always, it depends on your data.  Below I’ll share some of the test results I came across when testing EHCC. The data used for these tests are a short version of a fact table.   The tests were performed on a quarter rack ExaData database machine (2 db nodes – with 16 cores each and 3 storage servers)
 
As you may already have noticed, English is my second language, so please excuse me for spelling, grammar and whatever errors you may find in this post ;-)
 
- Test block compression against EHCC compression tables
First let’s look at the time it took to create the test data and the compression rate.
 
-- None compressed table
SQL> create table he100 PARALLEL 64 as select /*+ PARALLEL 64 */ * from he100_load_test;
Table created.
 
Elapsed: 00:00:33.97  
Did not seem to be CPU bound - Saw CPU utilization around 10 - 25%.
 
-- Block compressed table
SQL> create table he100_block compress for all operations PARALLEL 64 as select /*+ PARALLEL 64 */ *
                      from he100_load_test;
 
Elapsed: 00:00:28.51
Noticed CPU utilization to be around 40 - 70%
 
-- Table creation with EHCC query option

Where can I download CentOS 2.1?

I need to download a copy of CentOS 2.1 (x86), but I can’t find it anywhere. I’ve been down the list of mirrors and they all list 2.1, but then have an empty tree below it.

If anyone knows how I can get hold of it please drop me a line.

Cheers

Tim…

I’m an Oakie now!

Yep, all of a sudden I was invited by Jonathan Lewis to the group of the most knowledgeable Oracle people in the world! I still can’t believe in this, but a number of e-mails reminds me I’m not sleeping and it’s not a dream. Thank you very much, Jonathan, for inviting me! Thanks to all [...]

I’m back

Long time no post… I post nothing for more than two months and there were reasons: I was on-site in Canada for 5 weeks in June/July, doing some stuff which I don’t do often in the back office – and most of the time quite busy; after that I spent two extremely hot and smoked [...]

HOWTO: Merge files under Windows

Small “howto”, because I always forget.

Today I needed to merge to Linux tar files on Windows. I downloaded the two Oracle VM Templates for Oracle Business Intelligence Enterprise Edition (OBIEE). After unzipping them you get two tar files called

  • OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file1of2
  • OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file1of2

To be able to merge them and then “untar” those files, under Linux or Unix you would do something like:

 
cat #66cc66;">{file01#66cc66;">} #66cc66;">{file02#66cc66;">}  | tar -xvz
 
cat OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file1of2 OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file2of2| tar -xvz
.

…with other words, you would “cat” the first and second file into a file and then “untar”-ed it on the fly via the “tar -xvz”. In Windows you would do this via the following command, that is the first “cat” part, merging the files, via:

 
#b1b100; font-weight: bold;">copy /B #66cc66;">{file01#66cc66;">} #66cc66;">{file02#66cc66;">} #66cc66;">{newfile#66cc66;">}
 
#b1b100; font-weight: bold;">copy /B OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file1of2 + OVM_EL4U5_X86_PVM_10gR3BIEE.tgz.file2of2 OVM_EL4U5_X86_PVM_10gR3BIEE.tgz
.

the Windows equivalent of the Linux/Unix

Subscribers

Some time ago I added the “subscribe” option to the right-hand panel to allow people to register for automatic email whenever I posted a new article. (I’ve also checked how easy it is to unsubscribe if you change your mind  - and it’s very easy)

Since then I haven’t been paying attention to how many people have subscribed – but I noticed today that the total number of active subscribers has gone over 250, which is quite nice.

If you haven’t noticed the option you might want to think about it:

  • benefit – you don’t have to check for new posts;
  • drawback – you don’t get any notification of comments on posts – unless you also subscribe to individual posts

Update 31st Aug 2010: Following the comments about RSS feeds, I’ve added a poll to this article to make it easier for people to express an opinion. If you also want to make a comment about which is better, feel free, but if you just want to register a preference it just takes a couple of clicks.

Update 1st Sept 2010: After 24 hours the votes have come in at roughly 2 to 1 in favour of full feeds – so I’ve changed the syndication settings to full feed, showing comment count.

Update 24th November 2010: WordPress keeps adding little details to their product – and I discovered this morning that the latest change is that they can now send email to a blog owner every time someone registers as a new subscriber. This prompted me to check how many subscribers I have – and it’s just gone up to 347. (I’ve decided to tell myself that this is why my viewing stats seem to have dropped off slightly – more people have decided to do the efficient thing by subscribing and then just reading the articles, so they spend less time browsing the blog and following recent comments, and more time doing their job.)