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|
# frozen_string_literal: true
# An InternalId is a strictly monotone sequence of integers
# generated for a given scope and usage.
#
# The monotone sequence may be broken if an ID is explicitly provided
# to `#track_greatest`.
#
# For example, issues use their project to scope internal ids:
# In that sense, scope is "project" and usage is "issues".
# Generated internal ids for an issue are unique per project.
#
# See InternalId#usage enum for available usages.
#
# In order to leverage InternalId for other usages, the idea is to
# * Add `usage` value to enum
# * (Optionally) add columns to `internal_ids` if needed for scope.
class InternalId < ApplicationRecord
extend Gitlab::Utils::StrongMemoize
belongs_to :project
belongs_to :namespace
enum usage: Enums::InternalId.usage_resources
validates :usage, presence: true
scope :filter_by, -> (scope, usage) do
where(**scope, usage: usage)
end
class << self
def track_greatest(subject, scope, usage, new_value, init)
build_generator(subject, scope, usage, init).track_greatest(new_value)
end
def generate_next(subject, scope, usage, init)
build_generator(subject, scope, usage, init).generate
end
def reset(subject, scope, usage, value)
build_generator(subject, scope, usage).reset(value)
end
# Flushing records is generally safe in a sense that those
# records are going to be re-created when needed.
#
# A filter condition has to be provided to not accidentally flush
# records for all projects.
def flush_records!(filter)
raise ArgumentError, "filter cannot be empty" if filter.blank?
where(filter).delete_all
end
def internal_id_transactions_increment(operation:, usage:)
self.internal_id_transactions_total.increment(
operation: operation,
usage: usage.to_s,
in_transaction: InternalId.connection.transaction_open?.to_s
)
end
def internal_id_transactions_total
strong_memoize(:internal_id_transactions_total) do
name = :gitlab_internal_id_transactions_total
comment = 'Counts all the internal ids happening within transaction'
Gitlab::Metrics.counter(name, comment)
end
end
private
def build_generator(subject, scope, usage, init = nil)
ImplicitlyLockingInternalIdGenerator.new(subject, scope, usage, init)
end
end
class ImplicitlyLockingInternalIdGenerator
# Generate next internal id for a given scope and usage.
#
# For currently supported usages, see #usage enum.
#
# The method implements a locking scheme that has the following properties:
# 1) Generated sequence of internal ids is unique per (scope and usage)
# 2) The method is thread-safe and may be used in concurrent threads/processes.
# 3) The generated sequence is gapless.
# 4) In the absence of a record in the internal_ids table, one will be created
# and last_value will be calculated on the fly.
#
# subject: The instance or class we're generating an internal id for.
# scope: Attributes that define the scope for id generation.
# Valid keys are `project/project_id` and `namespace/namespace_id`.
# usage: Symbol to define the usage of the internal id, see InternalId.usages
# init: Proc that accepts the subject and the scope and returns Integer|NilClass
attr_reader :subject, :scope, :scope_attrs, :usage, :init
RecordAlreadyExists = Class.new(StandardError)
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?
unless InternalId.usages.has_key?(usage.to_s)
raise ArgumentError, "Usage '#{usage}' is unknown. Supported values are #{InternalId.usages.keys} from InternalId.usages"
end
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
InternalId.internal_id_transactions_increment(operation: :generate, usage: usage)
next_iid = update_record!(subject, scope, usage, arel_table[:last_value] + 1)
return next_iid if next_iid
create_record!(subject, scope, usage, initial_value(subject, scope) + 1)
rescue RecordAlreadyExists
retry
end
# Reset tries to rewind to `value-1`. This will only succeed,
# if `value` stored in database is equal to `last_value`.
# value: The expected last_value to decrement
def reset(value)
return false unless value
InternalId.internal_id_transactions_increment(operation: :reset, usage: usage)
iid = update_record!(subject, scope.merge(last_value: value), usage, arel_table[:last_value] - 1)
iid == value - 1
end
# Create a record in internal_ids if one does not yet exist
# and set its new_value if it is higher than the current last_value
def track_greatest(new_value)
InternalId.internal_id_transactions_increment(operation: :track_greatest, usage: usage)
function = Arel::Nodes::NamedFunction.new('GREATEST', [
arel_table[:last_value],
new_value.to_i
])
next_iid = update_record!(subject, scope, usage, function)
return next_iid if next_iid
create_record!(subject, scope, usage, [initial_value(subject, scope), new_value].max)
rescue RecordAlreadyExists
retry
end
private
def update_record!(subject, scope, usage, new_value)
stmt = Arel::UpdateManager.new
stmt.table(arel_table)
stmt.set(arel_table[:last_value] => new_value)
stmt.wheres = InternalId.filter_by(scope, usage).arel.constraints
InternalId.connection.insert(stmt, 'Update InternalId', 'last_value')
end
def create_record!(subject, scope, usage, value)
scope[:project].save! if scope[:project] && !scope[:project].persisted?
scope[:namespace].save! if scope[:namespace] && !scope[:namespace].persisted?
attributes = {
project_id: scope[:project]&.id || scope[:project_id],
namespace_id: scope[:namespace]&.id || scope[:namespace_id],
usage: usage_value,
last_value: value
}
result = InternalId.insert(attributes)
raise RecordAlreadyExists if result.empty?
value
end
def arel_table
InternalId.arel_table
end
def initial_value(subject, scope)
raise ArgumentError, 'Cannot initialize without init!' unless init
# `init` computes the maximum based on actual records. We use the
# primary to make sure we have up to date results
Gitlab::Database::LoadBalancing::Session.current.use_primary do
instance = subject.is_a?(::Class) ? nil : subject
init.call(instance, scope) || 0
end
end
def usage_value
@usage_value ||= InternalId.usages[usage.to_s]
end
end
end
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