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# frozen_string_literal: true
class BackgroundMigrationWorker
include ApplicationWorker
# The minimum amount of time between processing two jobs of the same migration
# class.
#
# This interval is set to 2 or 5 minutes so autovacuuming and other
# maintenance related tasks have plenty of time to clean up after a migration
# has been performed.
def self.minimum_interval
2.minutes.to_i
end
# Performs the background migration.
#
# See Gitlab::BackgroundMigration.perform for more information.
#
# class_name - The class name of the background migration to run.
# arguments - The arguments to pass to the migration class.
def perform(class_name, arguments = [])
should_perform, ttl = perform_and_ttl(class_name)
if should_perform
Gitlab::BackgroundMigration.perform(class_name, arguments)
else
# If the lease could not be obtained this means either another process is
# running a migration of this class or we ran one recently. In this case
# we'll reschedule the job in such a way that it is picked up again around
# the time the lease expires.
self.class
.perform_in(ttl || self.class.minimum_interval, class_name, arguments)
end
end
def perform_and_ttl(class_name)
if always_perform?
# In test environments `perform_in` will run right away. This can then
# lead to stack level errors in the above `#perform`. To work around this
# we'll just perform the migration right away in the test environment.
[true, nil]
else
lease = lease_for(class_name)
perform = !!lease.try_obtain
# If we managed to acquire the lease but the DB is not healthy, then we
# want to simply reschedule our job and try again _after_ the lease
# expires.
if perform && !healthy_database?
database_unhealthy_counter.increment
perform = false
end
[perform, lease.ttl]
end
end
def lease_for(class_name)
Gitlab::ExclusiveLease
.new(lease_key_for(class_name), timeout: self.class.minimum_interval)
end
def lease_key_for(class_name)
"#{self.class.name}:#{class_name}"
end
def always_perform?
Rails.env.test?
end
# Returns true if the database is healthy enough to allow the migration to be
# performed.
#
# class_name - The name of the background migration that we might want to
# run.
def healthy_database?
return true unless Gitlab::Database.postgresql?
!Postgresql::ReplicationSlot.lag_too_great?
end
def database_unhealthy_counter
Gitlab::Metrics.counter(
:background_migration_database_health_reschedules,
'The number of times a background migration is rescheduled because the database is unhealthy.'
)
end
end
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