When used in rails, a middleware is added to the rack server which negatively affects performance.
CheckPending performance
On every rails request, including in production, the list of migrations is found via ActiveGraph::Migrations::Runner#latest_migration. This method transitively calls the files method, which checks the filesystem for migration files and parses the name of each migration.
In a production setting, the actual pending migrations check will only happen the first time the middleware runs, but the performance hit of calling latest_migration will be added to every request.
I noticed the performance hit of this call while profiling a test suit with stackprof flamegraphs. It seems to take more time than many queries! By instrumenting the call to latest_migration and measuring it with stackprof, I found that it accounted for 3.5% of the duration of one of our api request spec files. Each call takes approximately 5-7ms on my machine - longer than most sql or neo4j queries.
Configuration
Pending migrations checks are configured according to two configuration options:
skip_migration_check : defaults to nil, set to true in rails test environments. This flag is checked before checking for pending migrations in check_for_pending_migrations!. Documented in readthedocs
fail_on_pending_migrations: defaults to true in rails (all environments). Adds the ActiveGraph::Migrations::CheckPendingmiddleware, which causes the check to run on every request. Does not appear to be documented in readthedocs.
What could be improved
Rails.env == 'test'
In a rails test environment, skip_migration_check is set to nil (false), meaning no error will be raised, but fail_on_pending_migrations is set to true, meaning the middleware will be added anyway!
An improvement for this case would be to set fail_on_pending_migrations to false in rails test environments, or whenever skip_migration_check is set to false. There's really no need to run the middleware when it's never going to raise an error.
This will speed up rails test suites a bit, which is nice!
Rails.env == 'production'
Another improvement could be to modify the checkpending middleware to avoid repeated latest_migration calls in production. This could be done by either:
removing the middleware after the first check
caching latest_migration
Workaround
Setting config.neo4j.fail_on_pending_migrations to false will allow you to avoid the middleware altogether. This does however mean that you lose the protection it provides
When used in rails, a middleware is added to the rack server which negatively affects performance.
CheckPending performance
On every rails request, including in production, the list of migrations is found via ActiveGraph::Migrations::Runner#latest_migration. This method transitively calls the
filesmethod, which checks the filesystem for migration files and parses the name of each migration.In a production setting, the actual pending migrations check will only happen the first time the middleware runs, but the performance hit of calling
latest_migrationwill be added to every request.I noticed the performance hit of this call while profiling a test suit with stackprof flamegraphs. It seems to take more time than many queries! By instrumenting the call to
latest_migrationand measuring it with stackprof, I found that it accounted for 3.5% of the duration of one of our api request spec files. Each call takes approximately 5-7ms on my machine - longer than most sql or neo4j queries.Configuration
Pending migrations checks are configured according to two configuration options:
skip_migration_check: defaults to nil, set to true in rails test environments. This flag is checked before checking for pending migrations in check_for_pending_migrations!. Documented in readthedocsfail_on_pending_migrations: defaults to true in rails (all environments). Adds theActiveGraph::Migrations::CheckPendingmiddleware, which causes the check to run on every request. Does not appear to be documented in readthedocs.What could be improved
Rails.env == 'test'
In a rails test environment,
skip_migration_checkis set to nil (false), meaning no error will be raised, butfail_on_pending_migrationsis set to true, meaning the middleware will be added anyway!An improvement for this case would be to set
fail_on_pending_migrations to falsein rails test environments, or whenever skip_migration_check is set to false. There's really no need to run the middleware when it's never going to raise an error.This will speed up rails test suites a bit, which is nice!
Rails.env == 'production'
Another improvement could be to modify the checkpending middleware to avoid repeated latest_migration calls in production. This could be done by either:
caching latest_migration
Workaround
Setting
config.neo4j.fail_on_pending_migrationstofalsewill allow you to avoid the middleware altogether. This does however mean that you lose the protection it provides