performance

It has been a while that I have been attending Hotsos, although that is how it feels. In 2011 I flew to Hotsos to see, among others presentations from Maria Colgan, but I ended up being sick the whole week while learning on my hotel room to enjoy American TV. In 2012 I skipped Hotsos …

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A customer of mine run out of memory due to much server processes of dedicated connected client sessions. As an alternative I tried to explain the options between DEDICATED and SHARED SERVER concepts as an initial attempt/workaround for the client software problems. Looking around on the internet for pictures and or newbie documentation, I found …

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I was at a client site recently where one of the end-users seemed to have discovered a cunning strategy for optimising a critical SQL statement. His problem was that his query screen times out after 2 minutes, so any query he runs has to complete in less than two minutes or he doesn’t see the results. Unfortunately he had a particular query which took nearly 32 minutes from cold to complete – partly because it’s a seven-table join using ANSI OUTER joins, against tables ranging through the 10s of millions of rows and gigabytes of data – the (necessary) tablescan of the table that had to be first in the join order took 70 seconds alone.

Van 3 tot en met 7 maart vindt in Irving, Texas, het internationale Oracle Performance Symposium Hotsos plaats. Dit jaar belooft het symposium een garantstelling voor inhoudelijk hoogstaande presentaties en discussies, want naast presentaties van Tom Kyte, Cary Millsap, Maria Colgan en Steven Feuerstein over performance, worden er ook onderwerpen behandeld zoals Big Data, noSQL, …

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I've been meaning to write this blog post for a while now but never seemed to find the time. Hopefully this posting will be useful information for anyone that spends a lot of time tracing processes in Oracle from the Linux Operating System. I'm one of those people, so it was good to get to [...]

This blog post is an introduction to a few posts that can be grouped together under the banner of 'System Architecture'. Specifically, I'm referring here to Oracle Database System Architecture, not system architecture in general nor 'Oracle architecture' in general, which is an ever-growing beast. In this series of posts, I will take at look [...]

A new version 2.0 of the XPLAN_ASH utility introduced here is available for download.You can download the latest version here.The change log tracks the following changes:- Access check- Conditional compilation for different database versions- Additional activity summary- Concurrent activity information (what is/was going on at the same time)- Experimental stuff: Additional I/O summary- More pretty printing- Experimental stuff: I/O added to Average Active Session Graph (renamed to Activity Timeline)- Top Execution Plan Lines and Top Activities added to Activity Timeline- Activity Timeline is now also shown for serial execution when TIMELINE option is specified- From 11.2.0.2 on: We get the ACTUAL DOP from the undocumented PX_FLAGS colu

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).

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.