SQL Server Troubleshooting: Unusual Corruption in Databases
Microsoft SQL Server is preferred the most, when it comes to create databases at large scale, typically in organizations developing software as well as at the places where these software are used. SQL Server stores and manages massive amounts of data, including different data types and their corresponding values. In order for efficient and unproblematic access to data stored in various tables in SQL Server, the system must be free from every single issue that can lead to corruption or some like states of affairs in it.
When your system has any such issue, the odds for corruption or similar scenarios are more and they ultimately lead to database corruption. Such a catastrophic situation results in massive loss of data and money for organizations.
SQL Database Corruption
While going through manifold forum sites discussing SQL database corruption scenarios, I perceived that many users have mentioned similar issues coming across persistently. I gathered the underlined issues and went for a thorough research to be known to their causes and found out their corresponding fixes in the form of a third party SQL database repair tool. I am going to emphasize those issues here in this post, aiming for making increasing number of SQL users aware of them.
Corruption in FCB (File Control Block)
The term FCB is related to SQL database files and is associated with the very first page of the file. In some database servers, there is a single file that holds the information of all the databases, such as the complete information of the databases and their respective connectivity to the database server. This MDF file is prone to corruption due to several internal and external causes, like virus attacks, file system corruption, and the like. In such a scenario, the SQL Server also encounters technical issues and might get corrupt severely. SQL Server sometimes throws errors that notify internal issues, which ultimately causes issues, such as database fails to connect to the sever. You cannot do anything to get out of the trouble and have to endure the loss of data.
Corruption in Boot Page
Amongst a number of pages in SQL Server, Boot Page is the vital one and it is completely different from the FCB, as it holds the information like the most recent checkpoint. This checkpoint is essential from both recovery and consistency viewpoints and must be kept under sight. Any issue with the Page will lead to fatal problems that at the end of the day will cause SQL Server failing to come online. You may also see SQL Server throwing errors. The consequences of the trouble are quite similar to those of the FCB corruption, which in turn cause database inaccessibility. Besides, you got nothing to do to get out of the trouble.
Corruption in Consistency
The database log files are also quite important since they store complete information of the transactions committed, no matter whether they were committed successfully or failed after initiated once. Log files store all this information in a logical flow and might cause several issues when get corrupt. To get out of the trouble, you need to create new log files and create new database with the execution of Create database command. You might also come across a few similar issues again due to inconsistent data. However, the transactions would surely be recorded. Data backup plays key role in recognizing the modifications done in the new database as compared to that in the original database.
Corruption in GAM/ SGAM/ PFS Page
Another special category of pages in SQL Server is GAM/ SGAM and PFS Pages, which is used to follow both the extent and page allocations, containing crucial information (PFS) of different types. These pages often get corrupt when you shut down the system while SQL Server was online or data stored on the server was involved in transactions. Since SQL Server stores data of significant values, you must act carefully and responsibly to avoid such things and ultimately to avoid the odds for corruption, as such issues in SQL Server are beyond maintenance and there is not a single way you can get out of it.
As per the research done by me, you can overcome such issues only if you script out the database objects to the maximum, and then recreate a database.
Corruption in Clustered Index Leaf Level
The term Leaf Level refers to Zero level (Level [0]), which is associated with data in the table. In the master copy of this clustered index (with the Leaf Level), you cannot make transactions like database rebuild, in case it is corrupt or some records are missing throughout the database. In the availability of transaction logs between the restore media to the end, you can go for a single page restore. Well, the Enterprise edition enables completing the page restore online, thereby benefitting you a lot.
Corruption in the page results in availability of the useless data. In other words, though the data is still available in the database, but its values are changed due to checksum error. This might result in SQL Server stopped responding to the queries executed.
Resolution
SQL Server contains extremely valuable data when it comes to use the database server in organizations. The server works at the backend and responds to each query executed at the GUI end. Based on the types of queries executed, the database sometimes gives random results, which is certainly due to corruption or some like technical issues in it. Since the things at server side are beyond understanding of laymen, the same requires technical users or a third party SQL database repair utility to get the issues fixed efficiently.
Note:
The efficient and reliable way to avoid data loss due to corruption in SQL Server database, you must keep a recent backup copy of your database at a secure location.