VOODOO
20.09.2017

rollback internals

While researching redo log internals for V00D00 we had to face the fact, that we know shit about real transactional behavior. When I say "real", I mean – under the hood. Even with a very simple stuff like COMMIT and ROLLBACK we were constantly amazed by the internal mechanisms. Today let’s take ROLLBACK under the […]


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V00D00
21.08.2017

How Oracle stores numbers internally

Before you proceed, please check out this short article written by Tanel Poder: http://blog.tanelpoder.com/2010/09/02/which-number-takes-more-space-in-an-oracle-row/ In the documentation, you can find the following explanation about the internal numeric format: Oracle stores numeric data in variable-length format. Each value is stored in scientific notation, with 1 byte used to store the exponent and up to 20 bytes […]


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#ThanksOTN
11.10.2016

OTN Appreciation Day : pragma UDF

Joining the OTN Appreciation Day 🙂 I really like the new pragma UDF feature for PL/SQL – it makes me believe that context switches will be less painful in the future 🙂 I wrote a little bit more about it here: http://blog.ora-600.pl/2015/10/29/oracle-12c-pragma-udf-the-truth/ And Martin Widlake wrote a lot about it here: https://mwidlake.wordpress.com/2015/11/11/pragma-udf-some-current-limitations/


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PL/SQL
19.09.2016

Using DTrace to understand why PL/SQL packages can be faster than stored procedures (kgiPinObject)

I know – everyone knows, that PL/SQL packages are faster than stored procedures. If you’ll ask anyone at the training or in your dev team "what is better" – you’ll (almost) always hear: PL/SQL packages. But why exactly? The documentation says: The first time you invoke a package subprogram, Oracle Database loads the whole package […]


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kksParseCursor
14.09.2016

session cached cursors and the significance of PL/SQL (kksParseCursor)

Years pass by and I think that the more I’m trying to understand the Oracle RDBMS – the less I know. Recently I started to examine the behavior of session cursor cache and I noticed an interesting thing. But let’s start from the beginning like we should 🙂 The documentation says: About the Session Cursor […]


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opifch2
27.05.2016

Context switch – PL/SQL cursor loops and fetchsize vs opifch2

Well it has been a month since my last blog post, so I think it’s time to write something 🙂 Those context switches can be a real pain in the ass – there is a great article by Frits Hoogland about context switching from SQL to PL/SQL – you can read it here: https://fritshoogland.wordpress.com/2016/01/23/plsql-context-switch/ You […]


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AWK
16.03.2016

AWK to the rescue 2 – 10046+10053 = ?

I’ve created recently a script in AWK to create wait event histogram from 10046 trace file. The script can be found here. I thought that a good idea would be creating a little script to analyze the contents of 10053 and 10046 events together. So I wrote one 🙂 You can download it here: http://ora-600.pl/oinstall/format_10046_10053.awk […]


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AWK
08.03.2016

AWK to the rescue – wait event histogram from trace file

I wrote a very simple script in AWK to create wait event histogram (for db file scattered read, db file sequential read, direct path read and direct path read temp) based on 10046 trace file with wait events. Maybe someone will find it useful 🙂 The sample output looks like this: Enjoy 😉


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EXADATA
11.02.2016

Exadata – direct path write temp and flash disks

Some time ago one of my students asked me if temp segments are being written to flash disks on Exadata… Well I wasn’t sure 🙂 But recently I had some time to check it. Let’s create some query that will generate temp segment: Great. Now we have to do some tracing at the cell servers […]


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M7
08.02.2016

Sparc M7 vs Intel and P8

I had a pleasure to work with my colleagues from Oracle – Radosław Kut and Krzysztof Marciniak – at comparing the performance of In-Memory queries between Sparc M7, Intel® Xeon® X5670 and Intel® Xeon® E5-2699. You can find results of our findings in this presentation: https://www.oracle.com/webfolder/s/delivery_production/docs/FY16h1/doc17/DB12c-on-SPARC-M7.pdf Following their methodology I’d like to present appropriate results […]


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M7
27.01.2016

Oracle SPARC M7 – tracing DAX with DTrace and busstat

Thanks to Oracle I had a possibility to test the new Sparc M7 with DAX coprocessors to boost In-Memory performance. You can read about it here and here My first thought was – how to check if and when the DAX coprocessors are being used? When you have a POC for Exadata, you want to […]


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tuning
13.01.2016

oracle dblinks – performance considerations

Let’s imagine the following situation – you have a table called EMPLOYEES_TMP which is a global temporary table with a variable number of rows – totally nondeterministic. And there is a query which runs very often to compare primary key values between this table and a remote one (which is basically the same but not […]


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12c
17.12.2015

Oracle 12c – internals of threaded execution

At UKOUG Tech’15 (Super Sunday) there was a session called "12c: A Closer Look at the Multi-Process Multi-Threaded Model for Oracle on Linux/Unix" by Markus Flechtner. Since then I can’t stop thinking about the performance of this feature. Why Oracle decided to provide it? I did some tests regarding sort operations and threaded execution was […]


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12c
29.10.2015

Oracle 12c: PRAGMA UDF – the truth

Let’s check, why PRAGMA UDF makes execution faster, then regular function. C function responsible for calling a PL/SQL code from SQL is called "plsql_run": Now let’s try to create a new HR session and create a simple function which will multiple values by 2: From other terminal I will connect to the HR session with […]


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[PL] Browar z Wyrocznią
04.09.2015

Jak smakuje Browar z Wyrocznią

I było tak, że 31 dnia miesiąca sierpnia roku 2015, spotkali się entuzjaści Wyroczni w posiadłości AVIVA. I było tak, że dzierżąc kufle – po brzegi browarem wypełnione – zasiadło wielu aby posłuchać kilku, którzy chcieli się przemyśleniami swoimi podzielić. I stało się tak, że admin przepijał do dewelopera a deweloper do admina i pospołu dyskusja toczyła się wartka a […]


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12C
03.09.2015

12c – SQL plan directives

One of the new CBO features in database 12c is "sql plan directives". The main purpose of this functionality is to deliver better adaptive plans if object statistics does not reflect the reality. Quoting after documentation During SQL execution, if a cardinality misestimate occurs, then the database creates SQL plan directives. During SQL compilation, the […]


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I/O
17.07.2015

db file scattered read – MBRC and ASYNC IO on linux

Recently one of my students asked me if there is any correlation between the AU size in ASM diskgroup and parameter db_file_multiblock_read_count. I made some tests but results are very strange. I have 4 same tables, located in 4 different diskgroups: All tables are smaller then a hidden parameter "_small_table_threshold" so table access full on […]


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12c (Spatial)
03.05.2015

12c: Spatial Vector Acceleration

There is a new feature in Oracle Spatial 12c, called "Spatial Vector Acceleration". According to Oracle: One of the most notable improvements with Oracle Spatial and Graph 12c can be seen in performance increases in vector data operations. Enabling the Spatial Vector Acceleration feature (available with the Spatial option) dramatically improves the performance of commonly […]


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