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|
# frozen_string_literal: true
class DeduplicateEpicIids < ActiveRecord::Migration[6.0]
include Gitlab::Database::MigrationHelpers
DOWNTIME = false
INDEX_NAME = 'index_epics_on_group_id_and_iid'
disable_ddl_transaction!
class Epic < ActiveRecord::Base
end
class InternalId < ActiveRecord::Base
class << self
def generate_next(subject, scope, usage, init)
InternalIdGenerator.new(subject, scope, usage, init).generate
end
end
# Increments #last_value and saves the record
#
# The operation locks the record and gathers a `ROW SHARE` lock (in PostgreSQL).
# As such, the increment is atomic and safe to be called concurrently.
def increment_and_save!
update_and_save { self.last_value = (last_value || 0) + 1 }
end
private
def update_and_save(&block)
lock!
yield
save!
last_value
end
end
# See app/models/internal_id
class InternalIdGenerator
attr_reader :subject, :scope, :scope_attrs, :usage, :init
def initialize(subject, scope, usage, init = nil)
@subject = subject
@scope = scope
@usage = usage
@init = init
raise ArgumentError, 'Scope is not well-defined, need at least one column for scope (given: 0)' if scope.empty? || usage.to_s != 'epics'
end
# Generates next internal id and returns it
# init: Block that gets called to initialize InternalId record if not present
# Make sure to not throw exceptions in the absence of records (if this is expected).
def generate
subject.transaction do
# Create a record in internal_ids if one does not yet exist
# and increment its last value
#
# Note this will acquire a ROW SHARE lock on the InternalId record
record.increment_and_save!
end
end
def record
@record ||= (lookup || create_record)
end
def lookup
InternalId.find_by(**scope, usage: usage_value)
end
def usage_value
4 # see Enums::InternalId - this is the value for epics
end
# Create InternalId record for (scope, usage) combination, if it doesn't exist
#
# We blindly insert without synchronization. If another process
# was faster in doing this, we'll realize once we hit the unique key constraint
# violation. We can safely roll-back the nested transaction and perform
# a lookup instead to retrieve the record.
def create_record
raise ArgumentError, 'Cannot initialize without init!' unless init
instance = subject.is_a?(::Class) ? nil : subject
subject.transaction(requires_new: true) do # rubocop:disable Performance/ActiveRecordSubtransactions
InternalId.create!(
**scope,
usage: usage_value,
last_value: init.call(instance, scope) || 0
)
end
rescue ActiveRecord::RecordNotUnique
lookup
end
end
def up
duplicate_epic_ids = ApplicationRecord.connection.execute('SELECT iid, group_id, COUNT(*) FROM epics GROUP BY iid, group_id HAVING COUNT(*) > 1;')
duplicate_epic_ids.each do |dup|
Epic.where(iid: dup['iid'], group_id: dup['group_id']).last(dup['count'] - 1).each do |epic|
new_iid = InternalId.generate_next(epic,
{ namespace_id: epic.group_id },
:epics, ->(instance, _) { instance.class.where(group_id: epic.group_id).maximum(:iid) }
)
epic.update!(iid: new_iid)
end
end
add_concurrent_index :epics, [:group_id, :iid], unique: true, name: INDEX_NAME
end
def down
# only remove the index, as we do not want to create the duplicates back
remove_concurrent_index :epics, [:group_id, :iid], name: INDEX_NAME
end
end
|
