ActiveRecord::Turntable
ActiveRecord::Turntable is a database sharding extension for ActiveRecord.
Dependencies
activerecord(>=5.0.0, <6.0)
- Current latest stable branch is stable branch.
If you are using with older activerecord versions, use following versions.
- activerecord 4.x - use activerecord-turntable version 2.x.(stable-2-x branch)
- activerecord 3.x - use activerecord-turntable version 1.x.(stable-1-x branch)
Supported DBMS
MySQL only.
Installation
Add to Gemfile:
gem 'activerecord-turntable', '~> 4.4.1'
Run a bundle install:
bundle install
Run install generator:
bundle exec rails g active_record:turntable:install
generator creates #{Rails.root}/config/turntable.yml
Terminologies
Shard
Shard is a database which is horizontal partitioned.
Cluster
Cluster of shards. i.e) set of userdb1, userdb2, userdb3. Shards in the same cluster should have the same schema structure.
Master
Default ActiveRecord::Base's connection.
Sequencer
Turntable's sequence system for clustered database.
This keeps primary key ids to be unique each shards.
Example
Example Databases Structure
One main database(default ActiveRecord::Base connection) and three user databases sharded by user_id.
+-------+
| App |
+-------+
|
+---------+---------+---------+---------+
| | | | |
`--------` `-------` `-------` `-------` `-------`
| Master | |UserDB1| |UserDB2| |UserDB3| | SeqDB |
`--------` `-------` `-------` `-------` `-------`
Example Configuration
Edit DSL type configuration file(config/turntable.rb) or YAML configuration file(turntable.yml). And add database connection settings to database.yml.
See below example config.
- example turntable.rb
cluster :user_cluster do
# algorithm [algorithm name symbol(range|range_bsearch|modulo)]
algorithm :range_bsearch
# sequencer [sequence name] [sequence type] [*options hash]
sequencer :user_seq, :mysql, connection: :user_seq
# shard [range], to: [connection names in database.yml]
shard 1...100, to: :user_shard_1
shard 100...200, to: :user_shard_2
shard 200...2000000000, to: :user_shard_3
# If you are using modulo algorithm, pass integer sequence start with zero.
#
# shard 0, to: :user_shard_1
# shard 1, to: :user_shard_2
# shard 2, to: :user_shard_3
end
- example turntable.yml
development:
clusters:
user_cluster: # <-- cluster name
algorithm: range_bsearch # <-- `range`, `range_bsearch` or `modulo`
seq:
user_seq: # <-- sequencer name
seq_type: mysql # <-- sequencer type
connection: user_seq_1 # <-- sequencer database connection setting
shards:
- connection: user_shard_1 # <-- shard name
less_than: 100 # <-- shard range(like mysql partitioning) If you are using a modulo algorithm, it doesn't need it.
- connection: user_shard_2
less_than: 200
- connection: user_shard_3
less_than: 2000000000
- database.yml
connection_spec: &spec
adapter: mysql2
encoding: utf8
reconnect: false
pool: 5
username: root
password: root
socket: /tmp/mysql.sock
development:
<<: *spec
database: sample_app_development
seq: # <-- sequence database definition
user_seq_1:
<<: *spec
database: sample_app_user_seq_development
shards: # <-- shards definition
user_shard_1:
<<: *spec
database: sample_app_user1_development
user_shard_2:
<<: *spec
database: sample_app_user2_development
user_shard_3:
<<: *spec
database: sample_app_user3_development
About algorithms
- range, range_bsearch - distribute records by key range
algorithm :range_bsearch
shard 1...20_000, to: :user_shard_1
shard 20_000...40_000, to: :user_shard_2
shard 40_000...60_000, to: :user_shard_1
shard 60_000...80_000, to: :user_shard_2
shard 80_000...10_000_000, to: :user_shard_3
- modulo - distribute records by key modulo
algorithm :modulo
shard 0, to: :user_shard_1
shard 1, to: :user_shard_2
shard 2, to: :user_shard_3
- hash_slot - distribute records by key hashes
default hash function is Zlib.crc32(key.to_s)
algorithm :hash_slot
# Or specify hash function
# algorithm :hash_slot, hash_func: ->(key) { Zlib.adler32(key.to_s) }
shard 0...4096, to: :user_shard_1
shard 4096...8192, to: :user_shard_2
shard 8192...12288, to: :user_shard_3
shard 12288...16384, to: :user_shard_4
Slave support (experimental)
Slave enabled configuration examples:
- config/turntable.rb
cluster :user_cluster do
...
# shard [range], to: [connection names in database.yml]
shard 1...100, to: :user_shard_1, slaves: [:user_shard_1_1]
shard 100...200, to: :user_shard_2, slaves: [:user_shard_2_1]
shard 200...2000000000, to: :user_shard_3, slaves: [:user_shard_3_1]
end
- config/turntable.yml
development:
clusters:
user_cluster: # <-- cluster name
...
shards:
- connection: user_shard_1
less_than: 100
slaves:
- user_shard_1_1
- connection: user_shard_2
less_than: 200
slaves:
- user_shard_2_1
- connection: user_shard_3
less_than: 2000000000
slaves:
- user_shard_3_1
- config/database.yml
Add slave connection settings under shards
.
...
shards:
user_shard_1:
<<: *default
database: turntable_user_shard_1_test
user_shard_1_1:
<<: *default
database: turntable_user_shard_1_1_test
user_shard_2:
<<: *default
database: turntable_user_shard_2_test
user_shard_2_1:
<<: *default
database: turntable_user_shard_2_1_test
user_shard_3:
<<: *default
database: turntable_user_shard_3_test
user_shard_3_1:
<<: *default
database: turntable_user_shard_3_1_test
Slave usage:
User.with_slave {
# `User` model will use slave databases within this block.
}
User.with_master {
# `User` model will use master database within this block.
}
Example Migration
Generate a model:
bundle exec rails g model user name:string
And Edit migration file:
class CreateUsers < ActiveRecord::Migration
# Specify cluster executes migration if you need.
# Default, migration would be executed to all databases.
# clusters :user_cluster
def change
create_table :users do |t|
t.string :name
t.
end
create_sequence_for(:users) # <-- create sequence table
end
end
Then please execute rake tasks:
bundle exec rake db:create
bundle exec rake db:migrate
Those rake tasks would be executed to shards too.
Example Model
Add turntable [shard_key_name] to the model class:
class User < ApplicationRecord
turntable :user_cluster, :id
sequencer :user_seq
has_one :status
end
class Status < ApplicationRecord
turntable :user_cluster, :user_id
sequencer :user_seq
belongs_to :user
end
Usage
Creating
> User.create(name: "hoge")
(0.0ms) [Shard: user_seq_1] BEGIN
(0.3ms) [Shard: user_seq_1] UPDATE `users_id_seq` SET id=LAST_INSERT_ID(id+1)
(0.8ms) [Shard: user_seq_1] COMMIT
(0.1ms) [Shard: user_seq_1] SELECT LAST_INSERT_ID()
(0.1ms) [Shard: user_shard_1] BEGIN
[ActiveRecord::Turntable] Sending method: insert, sql: #<Arel::InsertManager:0x007f8503685b48>, shards: ["user_shard_1"]
SQL (0.8ms) [Shard: user_shard_1] INSERT INTO `users` (`created_at`, `id`, `name`, `updated_at`) VALUES ('2012-04-10 03:59:42', 2, 'hoge', '2012-04-10 03:59:42')
(0.4ms) [Shard: user_shard_1] COMMIT
=> #<User id: 2, name: "hoge", created_at: "2012-04-10 03:59:42", updated_at: "2012-04-10 03:59:42">
Retrieving
> user = User.find(2)
[ActiveRecord::Turntable] Sending method: select_all, sql: #<Arel::SelectManager:0x007f850466e668>, shards: ["user_shard_1"]
User Load (0.3ms) [Shard: user_shard_1] SELECT `users`.* FROM `users` WHERE `users`.`id` = 2 LIMIT 1
=> #<User id: 2, name: "hoge", created_at: "2012-04-10 03:59:42", updated_at: "2012-04-10 03:59:42">
Updating
> user.update_attributes(name: "hogefoo")
(0.1ms) [Shard: user_shard_1] BEGIN
[ActiveRecord::Turntable] Sending method: update, sql: UPDATE `users` SET `name` = 'hogefoo', `updated_at` = '2012-04-10 04:07:52' WHERE `users`.`id` = 2, shards: ["user_shard_1"]
(0.3ms) [Shard: user_shard_1] UPDATE `users` SET `name` = 'hogefoo', `updated_at` = '2012-04-10 04:07:52' WHERE `users`.`id` = 2
(0.8ms) [Shard: user_shard_1] COMMIT
=> true
Delete
> user.destroy
(0.2ms) [Shard: user_shard_1] BEGIN
[ActiveRecord::Turntable] Sending method: delete, sql: #<Arel::DeleteManager:0x007f8503677ea8>, shards: ["user_shard_1"]
SQL (0.3ms) [Shard: user_shard_1] DELETE FROM `users` WHERE `users`.`id` = 2
(1.7ms) [Shard: user_shard_1] COMMIT
=> #<User id: 2, name: "hogefoo", created_at: "2012-04-10 03:59:42", updated_at: "2012-04-10 04:07:52">
Counting
> User.count
[ActiveRecord::Turntable] Sending method: select_value, sql: #<Arel::SelectManager:0x007f9e82ccebb0>, shards: ["user_shard_1", "user_shard_2", "user_shard_3"]
(0.8ms) [Shard: user_shard_1] SELECT COUNT(*) FROM `users`
(0.3ms) [Shard: user_shard_2] SELECT COUNT(*) FROM `users`
(0.2ms) [Shard: user_shard_3] SELECT COUNT(*) FROM `users`
=> 1
Sequencer
Sequencer provides generating global IDs.
Turntable has follow 3 sequencers currently:
- :mysql - Use database table to generate ids.
- :barrage - Use barrage gem to generate ids
- :katsubushi - katsubushi sequencer backend
Mysql example
First, add configuration to turntable.yml and database.yml
- database.yml
development:
...
seq: # <-- sequence database definition
user_seq_1:
<<: *spec
database: sample_app_user_seq_development
- turntable.yml
development:
clusters:
user_cluster: # <-- cluster name
....
seq:
user_seq: # <-- sequencer name
seq_type: mysql # <-- sequencer type
connection: user_seq_1 # <-- sequencer database connection
Add below to the migration:
create_sequence_for(:users) # <-- this line creates sequence table named `users_id_seq`
Next, add sequencer definition to the model:
class User < ApplicationRecord
turntable :id
sequencer :user_seq # <-- this line enables sequencer module
has_one :status
end
Barrage example
First, add barrage gem to your Gemfile:
gem 'barrage'
Then, add configuration to turntable.yml:
- turntable.yml
development:
clusters:
user_cluster: # <-- cluster name
....
seq:
barrage_seq: # <-- sequencer name
seq_type: barrage # <-- sequencer type
options: # <-- options passed to barrage
generators:
- name: msec
length: 39 # MAX 17.4 years from start_at
start_at: 1396278000000 # 2014/04/01 00:00:00 JST
- name: redis_worker_id
length: 16
ttl: 300
redis:
host: '127.0.0.1'
- name: sequence
length: 9
Next, add sequencer definition to the model:
class User < ApplicationRecord
turntable :id
sequencer :barrage_seq # <-- this line enables sequencer module
has_one :status
end
Katsubushi example
katsubushi is available as a sequence server. ActiveRecord::Turntable accesses katsubushi via Dalli.
First, add dalli gem to your Gemfile:
gem 'dalli'
Then, add configuration to turntable.yml:
- turntable.yml
development:
clusters:
user_cluster: # <-- cluster name
....
seq:
katsubushi_seq: # <-- sequencer name
seq_type: katsubushi # <-- sequencer type
options: # <-- options passed to dalli
servers:
- host: localhost
port: 11212
- host: localhost
port: 11213
Next, add sequencer definition to the model:
class User < ApplicationRecord
turntable :id
sequencer :katsubushi_seq # <-- this line enables sequencer module
has_one :status
end
Transactions
Turntable has some transaction support methods.
shards_transaction
Pass AR::Base instances, shards_transaction
method suitable shards
user = User.find(2)
user3 = User.create(name: "hoge3")
User.shards_transaction([user, user3]) do
user.name = "hogehoge"
user3.name = "hogehoge3"
user.save!
user3.save!
end
cluster_transaction
When executing transaction on all shards in the cluster, use #{cluster_name}_transaction
method:
User.user_cluster_transaction do
# Transaction is opened all shards in "user_cluster"
end
Migration
If you specify cluster or shard, migration will be executed to the cluster(or shard) and master database.
Default, migrations will be executed to all databases.
to specify cluster:
class CreateUsers < ActiveRecord::Migration
clusters :user_cluster
....
end
to specify shard:
class CreateUsers < ActiveRecord::Migration
shards :user_shard_01
....
end
Limitations
- Queries includes "ORDER BY", "GROUP BY" and "LIMIT" clauses cannot be distributed.
- "has many through" and "habtm" relationships may returns unexpected results. ex)
User-Friend-User
relation
TIPS
Send query to a specific shard.
Use with_shard
method:
AR::Base.with_shard(shard1) do
# something queries to shard1
end
with_shard
method accepts following types to specify a shard:
- ActiveRecord::Turntable::Shard object
- AcitveRecord::Base object -
AR::Base#turntable_shard
will be used - Numeric, String - a shard key value
- Symbol - shard name symbol
To access shard objects, use below:
- AR::Base.connection.shards # {shard_name => shard_obj,....}
- AR::Base#turntable_shard # Returns current object's shard
- AR::Base.connection.shard_for(shard_key_value) #=> shard
Send query to all shards
Use with_all method:
User.with_all do
User.order("created_at DESC").limit(3).all
end # => Returns Array of results
Cannot specify error is raised between associations
Normally, activerecord-turntable detects shard keys on associated models, but auto-detection will fail with following conditions:
- foreign key column != shard key column
- Using different shard key names
For example:
class User
# shard key:
# foreign key: main_user_item_id
belongs_to :main_user_item, class_name: "UserItem", required: false
end
class UserItem
# shard key name: :user_id
turntable :user_cluster, :user_id
end
This example raises CannotSpecifyShardError
> user.main_user_item
User Load [Shard: master] (0.4ms) SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1
[ActiveRecord::Turntable] Error on Building Fader: SELECT `user_items`.* FROM `user_items` WHERE `user_items`.`id` = 2198059200000 LIMIT 1, on_method: select_all, err: cannot specifyshard for query: SELECT "user_items".* FROM `user_items` WHERE (`user_items`.`id` = 2198059200000) LIMIT 1
ActiveRecord::Turntable::CannotSpecifyShardError: cannot specify shard for query: SELECT "user_items".* FROM `user_items` WHERE (`user_items`.`id` = 2198059200000) LIMIT 1
Use foreign_shard_key option to pass a shard key condition:
-belongs_to :main_user_item, class_name: "UserItem"
+belongs_to :main_user_item, class_name: "UserItem", foreign_shard_key: :id
> user.main_user_item
User Load [Shard: master] (0.2ms) SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1
[ActiveRecord::Turntable] Sending method: select_all, sql: #<Arel::SelectManager:0x007f8080bd0670>, shards: ["user_shard_1"]
Changing UserItem's shard to user_shard_1
UserItem Load [Shard: user_shard_1] (0.2ms) SELECT `user_items`.* FROM `user_items` WHERE `user_items`.`user_id` = 1 AND `user_items`.`id` = 2198059200000 LIMIT 1
Changing UserItem's shard to master
=> #<UserItem id: 2198059200000, user_id: 1, item_id: 1, created_at: "2017-05-23 04:41:13", updated_at: "2017-05-23 04:41:13">
Performance Exception
To notice queries causing performance problem, Turntable has follow options.
- raise_on_not_specified_shard_query - raises on queries execute on all shards
- raise_on_not_specified_shard_update - raises on updates executed on all shards
Add to turntable.yml or turntable.rb:
development:
....
raise_on_not_specified_shard_query: true
raise_on_not_specified_shard_update: true
# Write on top level
raise_on_not_specified_shard_query true
raise_on_not_specified_shard_update true
Thanks
ConnectionProxy, Distributed Migration implementation is inspired by Octopus and DataFabric.
License
activerecord-turntable is released under the MIT license:
Copyright (c) 2012 Drecom Co.,Ltd.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.