ActiveRecord::Turntable

ActiveRecord::Turntable is a database sharding extension for ActiveRecord.

Dependencies

activerecord(>=5.0.0,

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:

“by gem ‘activerecord-turntable’, ‘~> 4.4.1’

“

Run a bundle install:

“by bundle install

“

Run install generator:

“sh 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

“by 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

“ml 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

“ml 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

“by 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

“by 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)

“by 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

“by 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

“ml 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.

“ml … 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:

“by 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:

“sh bundle exec rails g model user name:string

“

And Edit migration file:

“by 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.timestamps end create_sequence_for(:users) # <– create sequence table end end

“

Then please execute rake tasks:

“sh 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:

“by 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 => #

Maruku could not parse this XML/HTML: 
<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 => #

Maruku could not parse this XML/HTML: 
<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 => #

Maruku could not parse this XML/HTML: 
<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

“ml development: … seq: # <– sequence database definition user_seq_1: «: spec database: sample_app_user_seq_development

“

turntable.yml

“ml 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:

“by create_sequence_for(:users) # <– this line creates sequence table named users_id_seq

“

Next, add sequencer definition to the model:

“by 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:

“by gem ‘barrage’

“

Then, add configuration to turntable.yml:

turntable.yml

“ml 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:

“by 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:

“by gem ‘dalli’

“

Then, add configuration to turntable.yml:

turntable.yml

“ml 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:

“by 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

“by 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:

“by 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:

“by class CreateUsers < ActiveRecord::Migration clusters :user_cluster …. end

“

to specify shard:

“by 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:

“by 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:

“by 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:

“by 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

“by

user.main_user_item User Load Shard: master 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

“

“by

user.main_user_item User Load Shard: master 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 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

=> #

Maruku could not parse this XML/HTML: 
<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:

“ml development: …. raise_on_not_specified_shard_query: true raise_on_not_specified_shard_update: true

“

“by

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:

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.