[Awesome Ruby Gem] Managing Bootsnap Cache in Rails: Troubleshooting Common Issues

Managing Bootsnap Cache in Rails: Troubleshooting Common Issues

When working with Ruby on Rails applications, optimizing performance and ensuring smooth deployments are paramount. One powerful tool in the Rails ecosystem for speeding up boot times is Bootsnap, which caches expensive computations and can significantly reduce application startup times. However, like any caching mechanism, it can sometimes cause issues that developers need to address. In this blog post, we’ll explore a common issue related to Bootsnap caching and how to resolve it effectively.

Understanding the Issue: belongs_to Not Working After Column Type Change

Imagine you have a Rails application with a Patient model that belongs to a Department. The association is defined as follows:

class Patient < ApplicationRecord
belongs_to :department, optional: true

You try to access the department of the last patient in the database:


But instead of getting the department, you encounter an error:

undefined method 'department' for #<Patient:0x00007f78ff60918>
Did you mean? department_id

This issue often arises after changing the type of the reference column (department_id) in the database. Even though the migration might have run successfully, the Rails application does not recognize the association, leading to the above error.

The Role of Bootsnap Cache

Bootsnap caches various elements of the application to improve performance, including method definitions and ActiveRecord associations. When you change the type of a reference column, these cached definitions might not get updated immediately, leading to the observed error.

Solution: Clearing the Bootsnap Cache

To resolve this issue, you need to clear the Bootsnap cache so that the application can reload the updated definitions. This can be done by removing the cached files in the tmp/cache/ directory. Execute the following command in your terminal:

rm -fr tmp/cache/

By removing these cache files, you force Rails to rebuild the cache with the updated column definitions and associations. This should resolve the undefined method 'department' error.

Proactive Cache Management

Periodic Cache Cleanup

Bootsnap does not automatically clean up its cache, which means that over time, the cache can grow and potentially slow down your deployments. Depending on your deployment strategy, you might need to periodically purge the tmp/cache/bootsnap* files to maintain optimal performance. For instance, you can add a cleanup step in your deployment script:

rm -fr tmp/cache/bootsnap*

Regularly clearing the Bootsnap cache can help prevent issues related to stale or outdated cache data, ensuring that your application continues to run smoothly.

Deployment Considerations

If you notice that your deployments are progressively getting slower, it’s almost certainly due to the growing Bootsnap cache. Incorporating a cache cleanup step in your deployment process can help mitigate this issue. For example, in a Capistrano deployment script, you could add a task to clear the cache:

namespace :deploy do
desc 'Clear Bootsnap cache'
task :clear_bootsnap_cache do
on roles(:app) do
execute :rm, '-fr', release_path.join('tmp/cache/bootsnap*')

before 'deploy:restart', 'deploy:clear_bootsnap_cache'

By adding such a task, you ensure that each deployment starts with a clean cache, reducing the risk of cache-related issues.


Bootsnap is a valuable tool for improving the performance of Ruby on Rails applications, but it requires proper management to avoid potential issues. When encountering problems like the belongs_to association not working after a column type change, clearing the Bootsnap cache is a quick and effective solution. Additionally, incorporating regular cache cleanup in your deployment process can help maintain optimal performance and prevent deployment slowdowns. By understanding and managing Bootsnap’s cache, you can ensure a smoother and more reliable Rails development experience.