Class: Switchman::Shard

Inherits:
ActiveRecord::Base
  • Object
show all
Defined in:
app/models/switchman/shard.rb

Constant Summary collapse

IDS_PER_SHARD =

ten trillion possible ids per shard. yup.

10_000_000_000_000

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

._load(str) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 471

def self._load(str)
  lookup(str.to_i)
end

.activate(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 53

def activate(shards)
  old_shards = activate!(shards)
  yield
ensure
  active_shards.merge!(old_shards)
end

.activate!(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 60

def activate!(shards)
  old_shards = {}
  shards.each do |category, shard|
    next if category == :unsharded
    old_shards[category] = active_shards[category]
    active_shards[category] = shard
  end
  old_shards
end

.categories ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 25

def categories
  CATEGORIES.keys
end

.clear_cache ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 109

def clear_cache
  @cached_shards = {}
end

.current(category = :default) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 49

def current(category = :default)
  active_shards[category] || Shard.default
end

.default(reload = false) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 29

def default(reload = false)
  if !@default || reload
    # Have to create a dummy object so that several key methods still work
    # (it's easier to do this in one place here, and just assume that sharding
    # is up and running everywhere else).  This includes for looking up the
    # default shard itself. This also needs to be a local so that this method
    # can be re-entrant
    default = DefaultShard.instance

    # the first time we need a dummy dummy for re-entrancy to avoid looping on ourselves
    @default ||= default
    # forget our current shard activations - it might have "another" default shard serialized there
    active_shards.clear

    # Now find the actual record, if it exists; rescue the fake default if the table doesn't exist
    @default = Shard.find_by_default(true) || default rescue default
  end
  @default
end

.global_id_for(any_id, source_shard = nil) ⇒ Object

takes an id-ish, and returns an integral global id. returns nil if it can’t be interpreted



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# File 'app/models/switchman/shard.rb', line 392

def global_id_for(any_id, source_shard = nil)
  id = integral_id_for(any_id)
  return any_id unless id
  if id >= IDS_PER_SHARD
    id
  else
    source_shard ||= Shard.current
    source_shard.global_id_for(id)
  end
end

.integral_id_for(any_id) ⇒ Object

converts an AR object, integral id, string id, or string short-global-id to a integral id. nil if it can’t be interpreted



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# File 'app/models/switchman/shard.rb', line 339

def integral_id_for(any_id)
  case any_id
  when ::ActiveRecord::Base
    any_id.id
  when /^(\d+)~(\d+)$/
    local_id = $2.to_i
    # doesn't make sense to have a double-global id
    return nil if local_id > IDS_PER_SHARD
    $1.to_i * IDS_PER_SHARD + local_id
  when Fixnum, /^\d+$/
    any_id.to_i
  else
    nil
  end
end

.local_id_for(any_id) ⇒ Object

takes an id-ish, and returns a local id and the shard it’s local to. [nil, nil] if it can’t be interpreted. [id, nil] if it’s already a local ID



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# File 'app/models/switchman/shard.rb', line 358

def local_id_for(any_id)
  id = integral_id_for(any_id)
  return [nil, nil] unless id
  if id < IDS_PER_SHARD
    [id, nil]
  elsif shard = lookup(id / IDS_PER_SHARD)
    [id % IDS_PER_SHARD, shard]
  else
    [nil, nil]
  end
end

.lookup(id) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'app/models/switchman/shard.rb', line 70

def lookup(id)
  id_i = id.to_i
  return current if id_i == current.id || id == 'self'
  return default if id_i == default.id || id.nil? || id == 'default'
  id = id_i
  raise ArgumentError if id == 0

  cached_shards[id] ||= Shard.default.activate do
    # can't simply cache the AR object since Shard has a custom serializer
    # that calls this method
    attributes = ::Rails.cache.fetch(['shard', id].join('/')) do
      shard = find_by_id(id)
      if shard
        attributes = shard.attributes
        attributes.each_key do |key|
          attributes[key] = attributes[key].unserialize if attributes[key].is_a?(::ActiveRecord::AttributeMethods::Serialization::Attribute)
        end
      else
        :nil
      end
    end
    if attributes == :nil
      nil
    else
      shard = Shard.new
      if ::Rails.version < '4'
        shard.assign_attributes(attributes, :without_protection => true)
      else
        shard.assign_attributes(attributes)
      end
      shard.instance_variable_set(:@new_record, false)
      # connection info doesn't exist in database.yml;
      # pretend the shard doesn't exist either
      shard = nil unless shard.database_server
      shard
    end
  end
end

.partition_by_shard(array, partition_proc = nil) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 304

def partition_by_shard(array, partition_proc = nil)
  shard_arrays = {}
  array.each do |object|
    partition_object = partition_proc ? partition_proc.call(object) : object
    case partition_object
      when Shard
        shard = partition_object
      when ::ActiveRecord::Base
        if partition_object.respond_to?(:associated_shards)
          partition_object.associated_shards.each do |a_shard|
            shard_arrays[a_shard] ||= []
            shard_arrays[a_shard] << object
          end
          next
        else
          shard = partition_object.shard
        end
      when Fixnum, /^\d+$/, /^(\d+)~(\d+)$/
        local_id, shard = Shard.local_id_for(partition_object)
        local_id ||= partition_object
        object = local_id if !partition_proc
    end
    shard ||= Shard.current
    shard_arrays[shard] ||= []
    shard_arrays[shard] << object
  end
  # TODO: use with_each_shard (or vice versa) to get
  # connection management and parallelism benefits
  shard_arrays.inject([]) do |results, (shard, objects)|
    results.concat shard.activate { Array(yield objects) }
  end
end

.relative_id_for(any_id, source_shard, target_shard) ⇒ Object

takes an id-ish, and returns an integral id relative to target_shard. returns any_id itself if it can’t be interpreted



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# File 'app/models/switchman/shard.rb', line 372

def relative_id_for(any_id, source_shard, target_shard)
  local_id, shard = local_id_for(any_id)
  return any_id unless local_id
  shard ||= source_shard
  return local_id if shard == target_shard
  shard.global_id_for(local_id)
end

.shard_for(any_id, source_shard = nil) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 403

def shard_for(any_id, source_shard = nil)
  _, shard = local_id_for(any_id)
  shard || source_shard || Shard.current
end

.short_id_for(any_id) ⇒ Object

takes an id-ish, and returns a shortened global string id if global, and itself if local. returns any_id itself if it can’t be interpreted



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# File 'app/models/switchman/shard.rb', line 383

def short_id_for(any_id)
  local_id, shard = local_id_for(any_id)
  return any_id unless local_id
  return local_id unless shard
  "#{shard.id}~#{local_id}"
end

.with_each_shard(*args) ⇒ Object

Parameters

  • shards - an array or relation of Shards to iterate over

  • categories - an array of categories to activate

  • options -

    :parallel - true/false to execute in parallel, or a integer of how many
            sub-processes per database server. Note that parallel
            invocation currently uses forking, so should be used sparingly
            because errors are not raised, and you cannot get results back
:exception - :ignore, :raise, :defer (wait until the end and raise the first
            error), or a proc



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# File 'app/models/switchman/shard.rb', line 124

def with_each_shard(*args)
  raise ArgumentError("wrong number of arguments (#{args.length} for 0...3)") if args.length > 3

  unless default.is_a?(Shard)
    return Array(yield)
  end

  options = args.extract_options!
  if args.length == 1
    if Array === args.first && args.first.first.is_a?(Symbol)
      categories = args.first
    else
      scope = args.first
    end
  else
    scope, categories = args
  end

  parallel = case options[:parallel]
               when true
                 1
               when false, nil
                 0
               else
                 options[:parallel]
             end
  options.delete(:parallel)
  scope ||= Shard.order("database_server_id IS NOT NULL, database_server_id, id")

  if parallel > 0
    if scope.class == ::ActiveRecord::NamedScope::Scope
      # still need a post-uniq, cause the default database server could be NULL or Rails.env in the db
      database_servers = scope.reorder('database_server_id').select(:database_server_id).uniq.
          map(&:database_server).compact.uniq
      scopes = Hash[database_servers.map do |server|
        server_scope = server.shards.merge(scope)
        if parallel == 1
          subscopes = [server_scope]
        else
          subscopes = []
          total = server_scope.count
          ranges = []
          server_scope.find_ids_in_ranges(:batch_size => (total.to_f / parallel).ceil) do |min, max|
            ranges << [min, max]
          end
          # create a half-open range on the last one
          ranges.last[1] = nil
          ranges.each do |min, max|
            subscope = server_scope.where("id>=?", min)
            subscope = subscope.where("id<=?", max) if max
            subscopes << subscope
          end
        end
        [server, subscopes]
      end]
    else
      scopes = scope.group_by(&:database_server)
      if parallel > 1
        scopes = Hash[scopes.map do |(server, shards)|
          [server, shards.in_groups(parallel, false).compact]
        end]
      end
    end

    fd_to_name_map = {}
    fds = []
    pids = []
    exception_pipe = IO.pipe
    scopes.each do |server, subscopes|
      if subscopes.first.class != ::ActiveRecord::NamedScope::Scope && subscopes.first.class != Array
        subscopes = [subscopes]
      end
      # only one process; don't bother forking
      if scopes.length == 1 && subscopes.length == 1
        exception_pipe.first.close
        exception_pipe.last.close
        return with_each_shard(subscopes.first, categories, options) { yield }
      end
      subscopes.each_with_index do |subscope, idx|
        if subscopes.length > 1
          name = "#{server.id} #{idx + 1}"
        else
          name = server.id
        end

        details = Open4.pfork4(lambda do
          begin
            ::ActiveRecord::Base.clear_all_connections!
            $0 = [$0, ARGV, name].flatten.join(' ')
            with_each_shard(subscope, categories, options) { yield }
          rescue Exception => e
            exception_pipe.last.write(Marshal.dump(e))
            exception_pipe.last.flush
            exit 1
          end
        end)
        # don't care about writing to stdin
        details[1].close
        fds.concat details[2..3]
        pids << details[0]
        fd_to_name_map[details[2]] = name
        fd_to_name_map[details[3]] = name
      end
    end
    exception_pipe.last.close

    while !fds.empty?
      ready, _ = IO.select(fds)
      ready.each do |fd|
        if fd.eof?
          fd.close
          fds.delete(fd)
          next
        end
        line = fd.readline
        puts "#{fd_to_name_map[fd]}: #{line}"
      end
    end
    pids.each { |pid| Process.waitpid2(pid) }
    # I'm not sure why, but we have to do this
    ::ActiveRecord::Base.clear_all_connections!
    # check for an exception; we only re-raise the first one
    # (all the sub-processes shared the same pipe, so we only
    # have to check the one)
    begin
      exception = Marshal.load exception_pipe.first
      raise exception
    rescue EOFError
      # No exceptions
    ensure
      exception_pipe.first.close
    end
    return
  end

  categories ||= []

  previous_shard = nil
  close_connections_if_needed = lambda do |shard|
    # prune the prior connection unless it happened to be the same
    if previous_shard && shard != previous_shard &&
      (shard.database_server != previous_shard.database_server || !previous_shard.database_server.shareable?)
      previous_shard.activate do
        if ::ActiveRecord::Base.connected? && ::ActiveRecord::Base.connection.open_transactions == 0
          ::ActiveRecord::Base.connection_pool.current_pool.disconnect!
        end
      end
    end
  end

  result = []
  exception = nil
  scope.each do |shard|
    # shard references a database server that isn't configured in this environment
    next unless shard.database_server
    close_connections_if_needed.call(shard)
    shard.activate(*categories) do
      begin
        result.concat Array(yield)
      rescue
        case options[:exception]
        when :ignore
        when :defer
          exception ||= $!
        when Proc
          options[:exception].call
        when :raise
          raise
        else
          raise
        end
      end
    end
    previous_shard = shard
  end
  close_connections_if_needed.call(Shard.current)
  raise exception if exception
  result
end

Instance Method Details

#==(rhs) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 527

def ==(rhs)
  return true if rhs.is_a?(DefaultShard) && default?
  super
end

#_dump(depth) ⇒ Object

custom serialization, since shard is self-referential



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# File 'app/models/switchman/shard.rb', line 467

def _dump(depth)
  self.id.to_s
end

#activate(*categories, &block) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 454

def activate(*categories, &block)
  shards = hashify_categories(categories)
  Shard.activate(shards, &block)
end

#activate!(*categories) ⇒ Object

for use from console ONLY



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# File 'app/models/switchman/shard.rb', line 460

def activate!(*categories)
  shards = hashify_categories(categories)
  Shard.activate!(shards)
  nil
end

#database_server ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 436

def database_server
  @database_server ||= DatabaseServer.find(self.database_server_id)
end

#database_server=(database_server) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 440

def database_server=(database_server)
  self.database_server_id = database_server.id
  @database_server = database_server
end

#description ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 445

def description
  [database_server.id, name].compact.join(':')
end

#drop_database ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 475

def drop_database
  return unless read_attribute(:name)
  begin
    adapter = self.database_server.config[:adapter]
    sharding_config = Switchman.config || {}
    drop_statement = sharding_config[adapter].try(:[], :drop_statement)
    drop_statement ||= sharding_config[:drop_statement]
    if drop_statement
      drop_statement = Array(drop_statement).dup.
          map { |statement| statement.gsub('%{db_name}', self.name) }
    end

    case adapter
      when 'mysql', 'mysql2'
        self.activate do
          ::Shackles.activate(:deploy) do
            drop_statement ||= "DROP DATABASE #{self.name}"
            Array(drop_statement).each do |stmt|
              ::ActiveRecord::Base.connection.execute(stmt)
            end
          end
        end
      when 'postgresql'
        self.activate do
          ::Shackles.activate(:deploy) do
            # Shut up, Postgres!
            conn = ::ActiveRecord::Base.connection
            old_proc = conn.raw_connection.set_notice_processor {}
            begin
              drop_statement ||= "DROP SCHEMA #{self.name} CASCADE"
              Array(drop_statement).each do |stmt|
                ::ActiveRecord::Base.connection.execute(stmt)
              end
            ensure
              conn.raw_connection.set_notice_processor(&old_proc) if old_proc
            end
          end
        end
      when 'sqlite3'
        File.delete(self.name) unless self.name == ':memory:'
    end
  rescue
    logger.info "Drop failed: #{$!}"
  end
end

#global_id_for(local_id) ⇒ Object

takes an id local to this shard, and returns a global id



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# File 'app/models/switchman/shard.rb', line 522

def global_id_for(local_id)
  return nil unless local_id
  local_id + self.id * IDS_PER_SHARD
end

#hash ⇒ Object

skip global_id.hash



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# File 'app/models/switchman/shard.rb', line 533

def hash
  id.hash
end

#name ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 427

def name
  read_attribute(:name) || default_name
end

#name=(name) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 431

def name=(name)
  write_attribute(:name, @name = name)
  remove_instance_variable(:@name) if name == nil
end

#shard ⇒ Object

Shards are always on the default shard



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# File 'app/models/switchman/shard.rb', line 450

def shard
  Shard.default
end