SQLite on Rails

When using SQLite in a Ruby on Rails application, optimizing its performance is critical, especially as the number of concurrent requests increases. SQLite's simplicity and embedded nature make it an attractive choice for single-node applications, but certain configurations are needed to ensure high performance in production environments.

A major concern with SQLite arises when handling concurrent write operations. By default, SQLite locks the entire database during a write operation, which can create performance bottlenecks as concurrent requests pile up. One solution is to enable SQLite's Write-Ahead Logging (WAL) mode, which allows reads and writes to occur simultaneously. This improves concurrency by preventing the database from being entirely locked during write operations, significantly enhancing performance in web applications.

Additionally, adjusting the busy_timeout configuration can mitigate issues with concurrent writes. This setting tells SQLite how long to wait before retrying a locked write operation. The default setting may not be sufficient under heavy load, so increasing the timeout can allow more queued write operations to succeed without failing. However, this approach can introduce delays, so finding the right balance is essential.

Moreover, to maximize concurrency, it is important to release Ruby's Global VM Lock (GVL) during database operations, particularly when waiting for SQLite write locks. When the GVL is not released, Rails workers handling multiple requests may be idle, preventing other workers from processing concurrent requests. Custom implementations of the busy_handler in SQLite can help by ensuring that the GVL is unlocked, allowing other workers to continue processing during database waits.

Recent updates in Rails 7.1 further optimize SQLite performance. For instance, the default configuration now uses WAL mode, and the synchronous mode is set to NORMAL, which reduces unnecessary disk syncing and enhances speed without significantly compromising data safety. Additionally, the cache_size is increased to 8MB, improving in-memory query performance, while the journal_size_limit is capped at 64MB, controlling the growth of the WAL file for better read performance.

These optimizations make SQLite a viable choice for production use, particularly in single-node applications where simplicity and reduced operational overhead are priorities. However, careful tuning is necessary to avoid potential bottlenecks in high-concurrency scenarios. By leveraging WAL mode, fine-tuning timeout settings, and updating the SQLite configuration, developers can significantly improve the performance and scalability of their Rails applications using SQLite

https://fractaledmind.github.io/2024/04/15/sqlite-on-rails-the-how-and-why-of-optimal-performance/