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# frozen_string_literal: true
class RescheduleMergeRequestDiffUsersBackgroundMigration < ActiveRecord::Migration[6.1]
include Gitlab::Database::MigrationHelpers
disable_ddl_transaction!
# The number of rows to process in a single migration job.
#
# The minimum interval for background migrations is two minutes. On staging we
# observed we can process roughly 20 000 rows in a minute. Based on the total
# number of rows on staging, this translates to a total processing time of
# roughly 14 days.
#
# By using a batch size of 40 000, we maintain a rate of roughly 20 000 rows
# per minute, hopefully keeping the total migration time under two weeks;
# instead of four weeks.
BATCH_SIZE = 40_000
MIGRATION_NAME = 'MigrateMergeRequestDiffCommitUsers'
class MergeRequestDiff < ActiveRecord::Base
self.table_name = 'merge_request_diffs'
end
def up
start = MergeRequestDiff.minimum(:id).to_i
max = MergeRequestDiff.maximum(:id).to_i
delay = BackgroundMigrationWorker.minimum_interval
Gitlab::Database::BackgroundMigrationJob
.where(class_name: MIGRATION_NAME)
.delete_all
# The table merge_request_diff_commits contains _a lot_ of rows (roughly 400
# 000 000 on staging). Iterating a table that large to determine job ranges
# would take a while.
#
# To avoid that overhead, we simply schedule fixed ranges according to the
# minimum and maximum IDs. The background migration in turn only processes
# rows that actually exist.
while start < max
stop = start + BATCH_SIZE
migrate_in(delay, MIGRATION_NAME, [start, stop])
Gitlab::Database::BackgroundMigrationJob
.create!(class_name: MIGRATION_NAME, arguments: [start, stop])
delay += BackgroundMigrationWorker.minimum_interval
start += BATCH_SIZE
end
end
def down
# no-op
end
end
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