Most Common Reasons for Corrupt SQLite Database

Generally, it’s very common to see corruption in the database files. Unlike other computer files, a database has a complicated file structure. Any sort of error or issue can corrupt the entire database with ease. Though an SQLite database is resistant to corruption, you can’t avoid it. Corruption is inevitable, i.e. certain to happen. In this article, I’ll show you the most common reasons for corrupt SQLite database. Also, I’ll help you learn how to perform SQLite recovery after corruption.

It’s believed that an SQLite database is highly resistant to corruption. Why? Whenever an application or the operating system crashes down, or a sudden power failure occurs in the middle of a transaction, this will leave the transaction partially written. But next time when the database file is accessed, the partially written transaction will be rolled back automatically. This recovery process is fully automatic, i.e. neither you nor the application needs to perform any action.

 Also Read: SQLite Error Database is Locked – How to Fix It

Corrupt SQLite Database

If you’re facing an uncommon issue while the transaction is being executed with SQLite database, this means the database file is corrupt. Whenever a transaction fails due to any reason, the action rolls back automatically. And when you reconnect to the SQLite Server, you have to start from the scratch. Have you ever faced such situation? Do you remember how you resolved it? There are many reasons for a corrupt SQLite database, but only one solution for SQLite recovery. Before we’ll learn how to repair SQLite database, let’s find out the most common reasons for corrupt SQLite database.

#1 – SQLite Database is being Overwritten

SQLite database file is an ordinary disk file. It’s highly possible that a process can open the file and overwrite it with junk data. Unluckily, the SQLite library can’t defend the file against any such action.

Run File Descriptor Continuously

If you continuously use a file descriptor after it has been closed, it may cause overwriting issues. The thread managed on SQLite log files may get overwritten by closing and re-opening the file descriptor. By this action, the data which goes to the server gets replaced and the SQLite database becomes corrupt afterward.

Backup or Restore while Transaction is in Active Mode

If any backup process is running at the backend of the system, it may create a backup of the SQLite database while the transaction is in active mode. The backup contains the logs of the previous state as well as earlier transactions.  And at the end, you’ll see the transactions IDs won’t match which may lead to corruption.

Delete Hot Journal

The auxiliary journal files play an important role in SQLite database recovery. But sometimes it may happen that the journal files are deleted and the server fails to find them. In such a situation, there’s no hope left for automatic SQLite database recovery.

#2 – File Locking Problems

SQLite supports a feature to lock the database file in order to coordinate with concurrent processes. If you don’t lock the database, two different processes can make changes in a single database that may lead to file corruption.

Lock Details are Missing

File-system is the most reliable source to lock the database files. But it may have some irresolvable bugs due to which the locks don’t always behave like as they’re supposed to. It may cause a situation like “lock details are missing” and lead to data corruption in the SQLite database.

Canceling POSIX Advisory Lock

POSIX advisory locking is the default locking mechanism used by SQLite database running on UNIX platforms. But there’s a design quirk in the POSIX advisory locking that makes it prone to misuse and failure. Sometimes it may happen that the system call, Close(), interrupts the locking process and leads to corruption in the SQLite thread. If you’re linking multiple copies of the SQLite database, you’re likely to face corruption.

 Also Read: How to Repair SQLite Database and Restore SQLite Database

Two Processes using Different Locking Protocols

The two locking protocols, SQLite3 vfs and SQLite3 open v2() are well-known for SQLite database handling. If you’re using both these protocols while working with an SQLite database, the contradiction can take place for sure. For example, if one application is using POSIX advisory locks and another one is using dot-file locking, the two applications can’t see each other’s locks. Thus, they’re not able to coordinate database access, and this may give you a corrupt SQLite database.

Renaming/Unlinking Database 

Renaming or unlinking an open database file may result in abnormal behavior. For example, two processes have open connections to the same SQL database. One of them closes the connection and unlinks the file. And then it creates a new database in its place with the same name and reopens the new file. This will create confusion. The two processes will communicate with different database files of the same name. Though it looks a minor issue, it may corrupt SQLite database.

Numerous Links to the Same File

A single database file has multiple names if it has multiple links (either hard or soft). If two or multiple processes open the database by using different names, they need to use different rollback journals and WAL files. And when one process crashes down, there’s no way for another one to recover the transaction in progress. This is just because it’ll be looking for the appropriate journal in the wrong place.

#3 – Database Synchronization Failure

Sometimes it may happen that the sync command of SQLite Server is playing the role of I/O barrier instead of performing the true synchronization. This may result in failure and cause rollback actions further. This is called the violation of ACID property.

#4 – Storage Media Failure

Any unexpected changes in the content of the hard disk drive or any other storage media device may cause severe issues in SQLite database. Also, if there’s no free space in the storage media and you’re trying to write something into it, this may lead to SQLite database corruption.

SQLite Database Recovery

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Whenever corruption takes place in the SQLite database, there’s no way to open it or access the information anyhow. If you have the valid backup for the SQLite database, you can successfully restore your data from it. But if there’s no backup, you must look forward to a professional solution. Use SQLite Database Recovery software to repair SQLite database and perform SQLite recovery effortlessly. It supports SQLite database created by SQLite2 and SQLite3. Before purchasing the software, you should download the demo version for free evaluation. By using the demo version, you can scan corrupt SQLite database and check the preview of your data which you can actually recover from it. If you’re satisfied with the results, then only you should purchase the software.

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