How to resolve SQLite Error Code 5 “Database is Locked”

SQLite is a relational database management system that is contained in a C library. Rather than being a client-server database engine, it is embedded into the end-program which makes it fast and in contrast to many other database systems.

Whenever we try to develop an application with SQLite, sometimes we get an error SQLite Database is Locked. In this blog, you will find all possible solutions to resolve this issue.

Various Reasons Behind Database is Locked

This error occurs whenever an SQLite user performs two inappropriate transactions or operations in a database on the same data connection.

The error message indicates that a similar operation can not be performed as there is an encounter with the transaction using the same database connection or a different database connection using a shared cache.

Different scenarios:

Different scenarios in which one can encounter this error are given below:

• When you use a table to write and on which the SELECT operations are previously active.
• The database gets locked in a situation when you try to DROP or CREATE an index or table while the SELECT statement is still in a pending state. The main reason behind it is the misconception of the users that if the Sqlite3_() returns the SQLITE_DONE value, the SELECT statement is finished. However, there is a different scenario because the SELECT statement is not considered to be completed until Sqlite3_reset() or Sqlite3_finalize() are called.
• When you try to  SELECT operations on the same table at the same time in an application having multiple threads and SQLite is not allowed for the same.

Manual Methods to Fix SQLite Database is Locked Error

It becomes really annoying whenever this SQLite_locked error occurs but using some of the mentioned methods, you can easily unlock the SQLite database.

1. By Creating Backup Having No Locks.

To remove the error code 5 from the SQLite database, the best way is to create a backup of the database having no locks. After creating a backup, just replace the original one with the backup copy. After that execute the below script to do so:

Note- Here, db.SQLite is meant to be an SQLite database file.

$Sqlite3 .db.Sqlite

Sqlite> .backup main backup.Sqlite

Sqlite> .exit

In the same directory, you will get the newly created backup file. Now swap the old file with this new file and execute the further script.

$mv .db.SQLite old.Sqlite

$mv backup.Sqlite .db.Sqlite

After the execution of the above script just check that the database is open allowing for both Read and Write. Then delete the old database file and you are good to go. 

2. Rewrite The Code:

SQLite is a “lite” database for real-world implementation. Whenever we try to make the database handle concurrency more than the default configuration, you can get errors. Therefore, rewriting the code for reducing concurrency can help to unlock the SQLite Database. By doing so you can also ensure that the transactions are not long-lived.

3. Increase Default Timeout:

If a transaction takes too much time then it can block the other threads from accessing the database. In the worst-case scenario, several threads can deadlock while waiting for each other’s completion. For this issue, SQLite has a lock timeout. If it detects that a thread is waiting for a lock for more than the default time(5 seconds), it stops the process and we face the SQLite DB is locked error.

To repair this error, you can increase the timeout value from the timeout database option.

Alternate Solution to resolve the SQLite error

If you are finding difficulty in manual methods, then you can use the alternate method of using an SQLite Database Recovery software. It recovers all the SQLite databases and fixes the corruptions in the database created by both SQLite2 and SQLite3 easily. Also, it is an efficient tool with an advanced algorithm that can effectively restore the SQLite Database.

Conclusion

In this article, I have discussed the SQLite error Database is locked. In addition to this, the reasons behind its occurrence and the possible manual and automated methods to resolve this particular error are also discussed. Go through these solutions as per your choice. If you have any other queries regarding the process, then do let me know, I’ll do my best to help you out. I hope this article is able to resolve your issue.

 

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