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# frozen_string_literal: true
module Gitlab
module BackgroundMigration
# Background migration that extends CopyColumn to update the value of a
# column using the value of another column in the same table.
#
# - The {start_id, end_id} arguments are at the start so that it can be used
# with `queue_background_migration_jobs_by_range_at_intervals`
# - Provides support for background job tracking through the use of
# Gitlab::Database::BackgroundMigrationJob
# - Uses sub-batching so that we can keep each update's execution time at
# low 100s ms, while being able to update more records per 2 minutes
# that we allow background migration jobs to be scheduled one after the other
# - We skip the NULL checks as they may result in not using an index scan
# - The table that is migrated does _not_ need `id` as the primary key
# We use the provided primary_key column to perform the update.
class CopyColumnUsingBackgroundMigrationJob
include Gitlab::Database::DynamicModelHelpers
PAUSE_SECONDS = 0.1
# start_id - The start ID of the range of rows to update.
# end_id - The end ID of the range of rows to update.
# table - The name of the table that contains the columns.
# primary_key - The primary key column of the table.
# copy_from - The column containing the data to copy.
# copy_to - The column to copy the data to.
# sub_batch_size - We don't want updates to take more than ~100ms
# This allows us to run multiple smaller batches during
# the minimum 2.minute interval that we can schedule jobs
def perform(start_id, end_id, table, primary_key, copy_from, copy_to, sub_batch_size)
quoted_copy_from = connection.quote_column_name(copy_from)
quoted_copy_to = connection.quote_column_name(copy_to)
parent_batch_relation = relation_scoped_to_range(table, primary_key, start_id, end_id)
parent_batch_relation.each_batch(column: primary_key, of: sub_batch_size) do |sub_batch|
sub_batch.update_all("#{quoted_copy_to}=#{quoted_copy_from}")
sleep(PAUSE_SECONDS)
end
# We have to add all arguments when marking a job as succeeded as they
# are all used to track the job by `queue_background_migration_jobs_by_range_at_intervals`
mark_job_as_succeeded(start_id, end_id, table, primary_key, copy_from, copy_to, sub_batch_size)
end
private
def connection
ActiveRecord::Base.connection
end
def mark_job_as_succeeded(*arguments)
Gitlab::Database::BackgroundMigrationJob.mark_all_as_succeeded(self.class.name, arguments)
end
def relation_scoped_to_range(source_table, source_key_column, start_id, stop_id)
define_batchable_model(source_table).where(source_key_column => start_id..stop_id)
end
end
end
end
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