GDB
28.01.2018

Oracle database block checksum XOR algorithm explained

Recently I’ve started to write my own clone of BBED to have something handy and useful in extreme cases when you have to go deep and fix stuff on low level (I have only like 2 such cases a year but each time it is really fun and a nice money 😉 ) When I’ll […]


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ODBV
21.12.2017

ODBVv2 – ghostdata busters

Some time ago I wrote a simple tool to learn about Oracle data block internals – ODBV. The series of articles can be found here: https://blog.ora-600.pl/?s=odbv&submit= and the github repo is here: https://github.com/ora600pl/odbv This is not a production tool but during the last session in Birmingham at UKOUG_TECH17 – where I was doing a presentation […]


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V00D00 & APUD
02.10.2017

Direct path insert and IOTs

(Please tell me that I’m not the only one who thinks "Index Organized Table" instead of "Internet Of Things" when hearing IOT…) This post is inspired by Connor McDonald and his blog post from a year ago about direct mode operations and IOTs. You can read it here: https://connor-mcdonald.com/2016/07/04/direct-mode-operations-on-iots/amp/ While writing a redo parser for […]


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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: https://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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VOODOO
24.07.2017

When UPDATE becomes an INSERT

During a research for VOODOO, we came across a lot of interesting stuff inside REDO. One of my favourites is an UPDATE, becoming an INSERT 🙂 So let’s see what has happened – I performed the following update on a sample table: The regular dump of redo log with an UPDATE looks like this: In […]


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VOODOO
28.05.2017

How to recover a dropped package from archivelogs – based on research for VOODOO engine

Sorry for long time without post, but we are writing with Marcin Rydz a new heterogenous replication product based on archivelogs and it’s consuming a looooooot of our time 🙂 Yes I know it’s nothing new on the market. There are other cool products and I know they’ll be probably be better. But we want […]


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ODBV
12.03.2017

ODBV improvements

Thanks to suggestions made by Frits Hoogland, I made some improvements to the ODBV. The new version can be found here: http://ora-600.pl/oinstall/odbv.x86_64 The changes are: Recognition of first, second and third level bitmap block Recognition of pagetable segment header Block number ranges on the left side The blocks will be coloured properly to belonging segment. […]


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ODBV
01.02.2017

back to the basics: ALTER TABLE MOVE vs SHRINK

It’s time for the next article with ODBV visualisation 🙂 This time let’s examine the difference between move and shrink – this is very common question on a lot of trainings. You can find a lot of great articles in the Internet regarding this subject but I think that visualisation really helps to understand what […]


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