1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
|
# 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
|
