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DBCC

Database Corruption Challenge #9 – How I Corrupted the Database.

I was asked how I caused the corruption in Database Corruption Challenge #9. Here is how I did it.

To cause the corruption, I used the undocumented DBCC WritePage, however the same thing could have been accomplished by detaching the database, opening it with a hex editor, and then re-attaching the db.

DBCC WritePage

WARNING: DBCC WritePage is a dangerous command, that should never be used on any production database. It may invalidate your ability to get support from Microsoft on issues that arise with that database going forward. It is not my intention to encourage anyone to use DBCC WritePage ever. This is just what I used to create a corrupt database, and since creating corrupt databases is not part of the role of most DBAs, you should not use DBCC WritePage. Consider yourself warned.

Read More »Database Corruption Challenge #9 – How I Corrupted the Database.

Corruption Challenge 1 – how I corrupted the database

Since the corruption challenge completed yesterday, I have had several request asking how I created the corrupt database. So here is the script that I used to create the Database Corruption Challenge 1.

First the initial setup. Most of this I stole from a query training session that I did several weeks ago. All I really needed was a table with some data in it.


CREATE DATABASE [CorruptionChallenge1];
GO

USE [CorruptionChallenge1];

CREATE TABLE Revenue
(
[id] INTEGER IDENTITY,
[DepartmentID] INTEGER,
[Revenue] INTEGER,
[Year] INTEGER,
[Notes] VARCHAR(300)
);

INSERT INTO Revenue ([DepartmentID], [Revenue], [Year])
VALUES (1,10030,1998),(2,20000,1998),(3,40000,1998),
 (1,20000,1999),(2,600400,1999),(3,500400,1999),
 (1,40050,2000),(2,400300,2000),(3,604000,2000),
 (1,30000,2001),(2,30000,2001),(3,703000,2001),
 (1,90000,2002),(2,200200,2002),(3,80000,2002),
 (1,10300,2003),(2,1000,2003), (3,900300,2003),
 (1,10000,2004),(2,10000,2004),(3,100300,2004),
 (1,208000,2005),(2,200200,2005),(3,203000,2005),
 (1,40000,2006),(2,30000,2006),(3,300300,2006),
 (1,709000,2007),(2,40000,2007),(3,400300,2007),
 (1,50000,2008),(2,50000,2008),(3,500300,2008),
 (1,20000,2009),(2,600030,2009),(3,600300,2009),
 (1,300700,2010),(2,70000,2010),(3,700300,2010),
 (1,80000,2011),(2,80000,2011),(3,800200,2011),
 (1,100030,2012),(2,90000,2012),(3,900300,2012),
 (1,10000,2013),(2,90000,2013),(3,900100,2013),
 (1,100400,2014),(2,900300,2014),(3,903000,2014),
 (1,102000,2015),(2,902000,2015),(3,902000,2015);

UPDATE Revenue SET [Notes] = CAST(NEWID() as VARCHAR(300)) + 'This is some varchar data just to fil out some pages... data pages are only 8k, therefore the more we fill up in each page, the more pages this table will flow into, thus simulating a larger table for the corruption example';

CREATE CLUSTERED INDEX [clustId] ON [dbo].[Revenue]
(
 [id] ASC
);

CREATE NONCLUSTERED INDEX [ncDeptIdYear] ON [dbo].[Revenue]
(
 [DepartmentID] ASC,
 [Revenue] ASC
);

CREATE NONCLUSTERED INDEX [ncBadNameForAnIndex] ON [dbo].[Revenue]
(
 [Year] ASC
)
INCLUDE ( [Notes]) ;

-- first lets look at the REVENUE table
SELECT *
 FROM Revenue;

Setup1

Read More »Corruption Challenge 1 – how I corrupted the database

A Weekend Full of Database Corruption

On Saturday morning, I announced the Database Corruption Challenge, and I had to abbreviate it as the DBCC, why not, acronym overloading isn’t always a bad thing.

There were 91 participants, 22 of which ended up with correct answers with no corruption and no data loss.

I created a database, with 3 bytes of corruption in one of the leaf node pages of a clustered index, however all I stated was that the database was corrupt, and it could be fixed with no data loss.

The number of different ways that people solved the problem was amazing. There were many attempts that did remove the corruption, and did recover all the rows, however many judged success as having the same number of rows as before, as a success. There were so many successful solutions that I think I will post one a day for the rest of the week, with the details explained. One solution even involved editing the database file on disk with a hex editor. I don’t have time to post all the good solutions right now.

 

The original corrupt database had been created on SQL Server 2014, but many people contacted me stating that they didn’t have SQL Server 2014 on their home computer, so I ended up creating a SQL Server 2008 version of the problem, but some were so driven to solve the challenge that they ended up installing SQL Server 2014 just to work the problem.

house1

Nice work John. Thanks for playing along, I hope you enjoyed the experience.  The next tweet from Mike Fal followed the post from John Morehouse.

nerd2

 

I hope that John took this comment from Mike Fal as a great compliments, however it was soon corrected by AJ Mendo that it is more geek than nerd.

aj1

Either way, geeks or nerds, it was a good learning experience for those involved, and for me having to evaluate each solution to determine if it was indeed a valid solution with no data loss. Personally I ended up restoring the corrupt database and testing different solutions over 50 times this weekend.

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Introducing the DataBase Corruption Challenge (DBCC) – Week 1 Challenge

corruption

Welcome to the DataBase Corruption Challenge, this is an about weekly blog challenge where I will post a corrupt SQL Server database with some details on what happened to it.

If at this point you are already a bit irked by my use of capitalization in the DataBase Corruption Challenge, and the acronym of DBCC that I have used to describe it, then you are already ahead of many people reading about this challenge. Welcome to the challenge.
The challenge will be to download the corrupt database and attempt to recover it. If you can recover it, please send me the steps to recover it, along with some proof that the database has been recovered. The goal each week will be the following:

Read More »Introducing the DataBase Corruption Challenge (DBCC) – Week 1 Challenge

SQL Sunday Fun – Word Search with SQL Server DBCC Commands

SQL_DBCC_Commands

The following DBCC commands are all hidden in the word search.  Be aware, some of the DBCC commands are undocumented.

CACHESTATS CHECKCATALOG CHECKCONSTRAINTS
CHECKDB CHECKFILEGROUP CHECKIDENT
CLEANTABLE DROPCLEANBUFFERS FLUSHPROCINDB
FREE FREEPROCCACHE FREESESSIONCACHE
FREESYSTEMCACHE INDEXDEFRAG OPENTRAN
OUTPUTBUFFER PAGE PROCCACHE
SHOWCONTIG SHRINKDATABASE TRACEON
TRACESTATUS UNPINTABLE UPDATEUSAGE
USEROPTIONS

END OF PUZZLE ————————-

See also:

For more information on DBCC Commands: