ODBV
30.12.2016

back to the basics: truncate table reuse storage vs drop storage

From time to time I get questions on my trainings, what is the difference between TRUNCATE TABLE and TRUNCATE TABLE DROP STORAGE… well, there is no difference because DROP STORAGE is default 😉 DROP STORAGE Specify DROP STORAGE to deallocate all space from the deleted rows from the table except the space allocated by the […]


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odbv
03.11.2016

Oracle Database Block Visualizer

Recently I wanted to demonstrate to some people on my training, how Oracle database maintains blocks in a datafile – what happens after truncate, truncate with drop storage clause, delete, regular insert, direct path insert and so on… I didn’t find any tool for that so I’ve written my own. It’s core code is based […]


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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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RICO
31.07.2016

how to recover dropped package

Sometimes you drop something by accident – you know, the syndrome called "An Enter Too Far". If you drop a table, the case is easy – you can use recyclebin to restore it. But when you drop a package or procedure… well, you have a problem 🙂 Of course, you could use a flashback query […]


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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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Exadata & SR-IOV
26.04.2016

Infiniband SR-IOV on Exadata OVM

Virtual hosts on Exadata with OVM are HVM and not PV. This is one of the limitations of Infiniband SR-IOV – can’t be used with PV. So there is a qemu used to emulate the hardware While accessing a physical device from within a DOMU we can see that actual work is being done on […]


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EXADATA+OVM
03.04.2016

Exadata & OVM: Unable to get map of the virtual network interfaces

This week I had a "pleasure" of reimaging Exadata server to use OVM. During this process we hit interesting problem – after the reimaging process there was no bridge at DOM0, corresponding to the client network – because of this, the OEDA sofware returned an error like this: The error was produced by this script: […]


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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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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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12c & external tables
10.02.2016

How to list files from directory using external table in 12c

I’ve wrote about privilege escalation with external tables in this post: https://blog.ora-600.pl/2014/12/23/simple-technics-of-privilege-escalation-part2-dbasysdba/ This time we will try to list all files within directory object, to which we have no EXECUTE privs. This is possible due to great new feature of database 12c that allows to use metacharacters to match multiple files in external table. I […]


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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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SECURITY
11.10.2015

Secure your database (part 1)

I’ve already showed you, how to escalate privileges in Oracle Databases. https://blog.ora-600.pl/2013/04/02/privilege-escalation-in-oracle-11gr2-part1/ https://blog.ora-600.pl/2014/12/23/simple-technics-of-privilege-escalation-part2-dbasysdba/ The question is – how to secure your database, if you don’t have EE or possibility to buy Oracle Database Vault or Oracle Advanced Security. Well – there’s always a DBA creativity 😉 For example – if you want to secure the […]


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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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RICO
03.09.2015

RICO

I’ve started the project called RICO – the tool, written in C++ for last resort data recovery. It can be used to extract data from corrupted datafiles and dump them in the form of text files. It is in the early development stage right now and the functionalities are narrowed to: Dump regular and partitioned […]


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