This project allows you to monkey patch ActiveRecord
(PostgreSQL) and auto-heal applications in production when PostgreSQL database fails over or when a cached column (in ActiveRecord
schema cache) is removed from the database from a migration in another process.
Install the gem and add to the application's Gemfile by executing:
$ bundle add rails-pg-adapter
If bundler is not being used to manage dependencies, install the gem by executing:
$ gem install rails-pg-adapter
# config/initializers/rails_pg_adapter.rb
RailsPgAdapter.configure do |c|
c.add_failover_patch = true
end
This will add the monkey patch which resets the ActiveRecord
connections in the connection pool when the database fails over. The patch will reset the connection and re-raise the error each time it detects that an exception related to a database failover is detected.
When the database is failing you can retry queries that are not in a transaction. The gem will perform a back off retry in establishing the connection. Once the back off is reached and no connection is found, it will bubble up the exception. Otherwise, the query will be retried with a new connection.
It is an opt-in functionality. You can supply your own back off figures for retries (in seconds) as following:
# config/initializers/rails_pg_adapter.rb
RailsPgAdapter.configure do |c|
c.add_failover_patch = true
c.reconnect_with_backoff = [0.5, 1, 2, 4, 8, 16] # seconds
...
end
# config/initializers/rails_pg_adapter.rb
RailsPgAdapter.configure do |c|
c.add_reset_column_information_patch = true
end
This will clear the ActiveRecord
schema cache and reset the ActiveRecord
column information memoized on the model. The patch will reset the relevant information and re-raise the error each time it detects that an exception related to a dropped column is raised.
During a database failover in production, the ActiveRecord
connection pool can become exhausted as queries are made against the database during the failover process. This can leave the ActiveRecord
connection pools with stale or bad connections, even after the database has successfully recovered. Recovering from this issue usually requires a rolling restart of the application processes or containers.
RailsPgAdapter
addresses this problem by resetting the connection pool and re-raises the original exception from an ActiveRecord
monkey patch. This allows the application to auto-heal from stale connections on its own (after database recovery) when performing queries for a new request, without requiring manual intervention.
Another issue with ActiveRecord
queries is PG::UndefinedColumn
, which occurs when an ActiveRecord
model includes a SELECT
query with the name of a column that has been dropped from a Rails migration. This can happen even if the column isn't being referenced anywhere in the code. It occurs when a model is using ignored_columns
, which prompts ActiveRecord
to perform a dedicated lookup of the allowed columns in a select, such as SELECT "users".name, "users".template_id...."
, instead of SELECT "users".*
. When a column like template_id
is dropped, PostgreSQL throws an undefined column error, which is bubbled up by ActiveRecord
into PG::UndefinedColumn
. Recovering from this issue also usually requires a rolling restart of the application processes or containers.
RailsPgAdapter
solves this second issue by resetting the ActiveRecord
schema cache and memoized model column information when it detects a PG::UndefinedColumn
raised from a monkey patch. Resetting the column information forces ActiveRecord
to refresh its schema cache by loading the table information from the database and no longer reference the dropped column for new queries, without requiring manual intervention.
- Install ruby 3.0
\curl -sSL https://get.rvm.io | bash
rvm install 3.0.0
rvm use 3.0.0
docker compose up -d
- to spin up postgres locallybundle exec rspec
to run the tests.- You can also run
bin/console
for an interactive prompt.
To install this gem onto your local machine, run bundle exec rake install
.
Bug reports and pull requests are welcome on GitHub at https://github.com/tines/rails-pg-adapter. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.
The gem is available as open source under the terms of the MIT License.
Everyone interacting in the RailsPgAdapter
project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.
- Bump version in
version.rb
- Update
CHANGELOG.md
- Push the changes to
main
- Run the release script with the new version
./bin/release.sh 0.2.0
- Note: It will ask for MFA.
- Create a new release - https://github.com/tines/rails-pg-adapter/releases/new