tips&tricks

In my last blog post I explained a XOR alghorithm that is used to count Oracle database block checksum.

I also wrote, that sometimes you are facing problems, that are unresolvable without a low-level knowledge. This is the story of this kind of situation. The story of misread documentation. The story of haste and hex.

About a year ago, I got a call from one company that did an APEX upgrade for one of their customers. Very big customer. Quite a big database and a very important one, working 24/7.

They told me that they upgraded APEX on a database with one PDB and a week later they tried to apply some patches and restarted the database. After the restart they got the following error:

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

• Internals
• Oracle
• Security
• tips&tricks

Some time ago I wrote a simple tool to learn about Oracle data block internals – ODBV.
The series of articles can be found here: http://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 using this tool – I came to the conclusion that with a little bit of work it could be used to trace ghost data in a database.

What is ghost data? This is very simple – each time we delete something or truncate or move, Oracle database is not removing data from our datafile – the blocks are "marked" for reuse and are not associated with any logical object in a database, but our data is still there.

If you work as a consultant, getting remote access to your customer is sometimes a nightmare!
Even when you’ll get one, there a times when you just want to get your job done and finish this nightmare.

For example, there are times when it is easier to dump a statspack repo and do offline analyzes. Unfortunately, it is not always possible. In this kind of circumstances, I ask my customer to generate the appropriate set of reports and send them to me for later analyzes. If you know the set of snapshot ids you want to analyze, you can use the following simple script to extract a set of statspack reports:

(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 V00D00 I had to investigate this subject very closely from a redo log perspective. And this will be the subject of my 10-minute lightning talk at Oak Table World 2017 at Oracle Open World!

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 investigation. According to documentation:

The ROLLBACK statement ends the current transaction and undoes any changes made during that transaction.

Cool. But what it means? First of all, you have to realize that all changes in redo logs are in a form of REDO RECORD which has its own address, known as RBA or RS_ID.

Sample RS_ID (RBA) looks like this: 0x00000a.00008c0f.006c

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

• 12c
• Internals
• Oracle
• tips&tricks

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

• 12c
• Internals
• Oracle
• tips&tricks

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

• tips&tricks

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

• Internals
• Oracle
• tips&tricks