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Solving the H2 Database Locking Issues in Spring Boot

Discover how to resolve H2 database locking issues that prevent data persistence in your Spring Boot applications, and learn best practices for managing database connections effectively. --- This video is based on the question https://stackoverflow.com/q/69121686/ asked by the user 'ksnortum' ( https://stackoverflow.com/u/980967/ ) and on the answer https://stackoverflow.com/a/69126023/ provided by the user 'ksnortum' ( https://stackoverflow.com/u/980967/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: H2 database not flushed because of file lock Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Solving the H2 Database Locking Issues in Spring Boot: A Practical Guide When developing applications with Spring Boot, many developers encounter various challenges related to database management, particularly when using the H2 database. One common problem arises with data not persisting after restarting the application—an issue that can be traced back to file locking during shutdown procedures. This guide will walk you through understanding and resolving such database locking issues. The Problem: Data Not Persisting In a training scenario using a Spring Boot REST API to manage recipes, you might encounter a frustrating obstacle where the data being entered into the H2 database disappears after restarting the application. This problem typically indicates that the database did not properly flush data changes, often the result of a file locking issue. From the specifics of the problem: Upon shutdown, the data is present in memory. Rebooting the application leads to lost data. A file lock appears to be preventing updates to the database file. What is Causing This? The root cause of this data loss is often linked to improper shutdown procedures in the Spring Boot application, leading to an attempt to access a locked database file. Users may note messages in their trace files indicating issues with the file being locked, which can stem from: An unclean shutdown of the application. Concurrent access to the database. Incorrect file lock settings in the application properties. The Solution: Debugging and Configuration Upon diagnosing the issue, you may find that simply changing file lock options isn’t sufficient. Here’s a structured approach to resolve the problem: Step 1: Debugging Configuration To identify the source of the problem, enable debugging in your application.properties file by adding: [[See Video to Reveal this Text or Code Snippet]] This enables detailed logging; upon analysis, you may discover messages highlighting that Spring is unintentionally dropping your tables during shutdown. Step 2: Adjust Hibernate Settings To stop Spring from dropping existing tables and instead update them as necessary, modify your application.properties to include: [[See Video to Reveal this Text or Code Snippet]] This command will ensure the schema is updated instead of dropped—preserving your data upon application restart. Step 3: File Lock Settings You might also want to experiment with file lock settings. Set the spring.datasource.url to use FILE_LOCK as follows: [[See Video to Reveal this Text or Code Snippet]] This explicitly indicates to H2 how to manage file locks, which can help prevent the locking issues experienced previously. Step 4: Clean Shutdown Ensure that you're always shutting down your Spring Boot application gracefully. Utilizing the Spring Boot actuator’s shutdown endpoint via Postman is the correct approach: Start the server from your IDE. Use it to create a new recipe. Verify its accessibility (should return the recipe without errors). Shutdown the server using actuator/shutdown. Restart the server and check for data persistence. Conclusion With these steps, you should be able to troubleshoot and resolve issues related to the H2 database locking in your Spring Boot projects. By enabling debugging, adjusting Hibernate settings, managing file locks, and ensuring clean shutdown procedures, you will significantly enhance your application’s reliability and data integrity. Remember, the key to successful database management lies not just in the code but also in the configurations and methods of interfacing with your data. Happy coding!