Class: Switchman::Shard

Inherits:
UnshardedRecord show all
Defined in:
lib/switchman/shard.rb

Constant Summary collapse

IDS_PER_SHARD =

ten trillion possible ids per shard. yup.

10_000_000_000_000
NIL_NIL_ID =

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. [nil, nil] if it’s a well formed id, but the shard it refers to does not exist

[nil, nil].freeze

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

._load(str) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 539

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

.activate(shards) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 62

def activate(shards)
  activated_classes = activate!(shards)
  yield
ensure
  activated_classes&.each do |klass|
    klass.connected_to_stack.pop
  end
end

.activate!(shards) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 71

def activate!(shards)
  activated_classes = nil
  shards.each do |klass, shard|
    next if klass == UnshardedRecord

    next unless klass.current_shard != shard.database_server.id.to_sym ||
                klass.current_switchman_shard != shard

    (activated_classes ||= []) << klass
    klass.connected_to_stack << { shard: shard.database_server.id.to_sym,
                                  klasses: [klass],
                                  switchman_shard: shard }
  end
  activated_classes
end

.active_shards ⇒ Object 



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# File 'lib/switchman/shard.rb', line 87

def active_shards
  sharded_models.filter_map do |klass|
    [klass, current(klass)]
  end.to_h
end

.clear_cache ⇒ Object 



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# File 'lib/switchman/shard.rb', line 114

def clear_cache
  cached_shards.clear
end

.current(klass = ::ActiveRecord::Base) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 57

def current(klass = ::ActiveRecord::Base)
  klass ||= ::ActiveRecord::Base
  klass.current_switchman_shard
end

.default(reload: false, with_fallback: false) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 21

def default(reload: false, with_fallback: 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

    # if we already have a default shard in place, and the caller wants
    # to use it as a fallback, use that instead of the dummy instance
    default = @default if with_fallback && @default

    # the first time we need a dummy dummy for re-entrancy to avoid looping on ourselves
    @default ||= default

    # Now find the actual record, if it exists
    @default = begin
      find_cached("default_shard") { Shard.where(default: true).take } || default
    rescue
      default
    end

    # make sure this is not erroneously cached
    if @default.database_server.instance_variable_defined?(:@primary_shard)
      @default.database_server.remove_instance_variable(:@primary_shard)
    end

    # and finally, check for cached references to the default shard on the existing connection
    sharded_models.each do |klass|
      klass.connection.shard = @default if klass.connected? && klass.connection.shard.default?
    end
  end
  @default
end

.drop_database(name) ⇒ Object

Drops a specific database/schema from the currently active connection



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# File 'lib/switchman/shard.rb', line 559

def self.drop_database(name)
  sharding_config = Switchman.config || {}
  drop_statement = sharding_config["postgresql"]&.[](:drop_statement)
  drop_statement ||= sharding_config[:drop_statement]
  drop_statement = Array(drop_statement).map { |statement| statement.gsub("%{name}", name) } if drop_statement

  ::GuardRail.activate(:deploy) do
    # Shut up, Postgres!
    conn = ::ActiveRecord::Base.connection
    old_proc = conn.raw_connection.set_notice_processor {}
    begin
      drop_statement ||= "DROP SCHEMA #{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

.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 'lib/switchman/shard.rb', line 365

def global_id_for(any_id, source_shard = nil)
  id = integral_id_for(any_id)
  return any_id unless id

  signed_id_operation(id) do |abs_id|
    if abs_id >= IDS_PER_SHARD
      abs_id
    else
      source_shard ||= Shard.current
      source_shard.global_id_for(abs_id)
    end
  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 'lib/switchman/shard.rb', line 292

def integral_id_for(any_id)
  case any_id
  when ::Arel::Nodes::Casted
    any_id = any_id.value
  when ::Arel::Nodes::BindParam
    any_id = any_id.value.value_before_type_cast
  end

  case any_id
  when ::ActiveRecord::Base
    any_id.id
  when /^(\d+)~(-?\d+)$/
    local_id = $2.to_i
    signed_id_operation(local_id) do |id|
      return nil if id > IDS_PER_SHARD

      ($1.to_i * IDS_PER_SHARD) + id
    end
  when Integer, /^-?\d+$/
    any_id.to_i
  end
end

.local_id_for(any_id) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 320

def local_id_for(any_id)
  id = integral_id_for(any_id)
  return NIL_NIL_ID unless id

  return_shard = nil
  local_id = signed_id_operation(id) do |abs_id|
    if abs_id < IDS_PER_SHARD
      abs_id
    elsif (return_shard = lookup(abs_id / IDS_PER_SHARD))
      abs_id % IDS_PER_SHARD
    else
      return NIL_NIL_ID
    end
  end
  [local_id, return_shard]
end

.lookup(id) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/switchman/shard.rb', line 93

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.zero?

  unless cached_shards.key?(id)
    cached_shards[id] = Shard.default.activate do
      find_cached(["shard", id]) { find_by(id: id) }
    end
  end
  cached_shards[id]
end

.partition_by_shard(array, partition_proc = nil) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 244

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 Integer, /^\d+$/, /^(\d+)~(\d+)$/
      local_id, shard = Shard.local_id_for(partition_object)
      local_id ||= partition_object
      object = local_id unless 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.wrap(yield objects) })
  end
end

.preload_cache ⇒ Object 



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# File 'lib/switchman/shard.rb', line 109

def preload_cache
  cached_shards.reverse_merge!(active_shards.values.index_by(&:id))
  cached_shards.reverse_merge!(all.index_by(&:id))
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 nil if it can’t be interpreted, or the integral version of the id if it refers to a shard that does not exist



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# File 'lib/switchman/shard.rb', line 341

def relative_id_for(any_id, source_shard, target_shard)
  integral_id = integral_id_for(any_id)
  local_id, shard = local_id_for(integral_id)
  return integral_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 'lib/switchman/shard.rb', line 379

def shard_for(any_id, source_shard = nil)
  return any_id.shard if any_id.is_a?(::ActiveRecord::Base)

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

.sharded_models ⇒ Object 



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# File 'lib/switchman/shard.rb', line 17

def sharded_models
  @sharded_models ||= [::ActiveRecord::Base, UnshardedRecord].freeze
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 'lib/switchman/shard.rb', line 355

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

.signed_id_operation(input_id) ⇒ Object

it’s tedious to hold onto this same kind of sign state and transform the result in multiple places, so here we can operate on the absolute value in a provided block and trust the sign will stay as provided. This assumes no consumer will return a nil value from the block.



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# File 'lib/switchman/shard.rb', line 284

def signed_id_operation(input_id)
  sign = input_id.negative? ? -1 : 1
  output = yield input_id.abs
  output * sign
end

.with_each_shard(*args, parallel: false, exception: :raise, output: :simple) ⇒ Object

Parameters

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

  • classes - an array of classes to activate

    parallel: - true/false to execute in parallel, or an integer of how many
            sub-processes. Note that parallel invocation currently uses
            forking.
exception: - :ignore, :raise, :defer (wait until the end and raise the first
            error), or a proc
output: - :simple, :decorated (with database_server_id:shard_name)

Raises:

  • (ArgumentError) 


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# File 'lib/switchman/shard.rb', line 128

def with_each_shard(*args, parallel: false, exception: :raise, output: :simple)
  raise ArgumentError, "wrong number of arguments (#{args.length} for 0...2)" if args.length > 2

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

  if args.length == 1
    if Array === args.first && args.first.first.is_a?(Class)
      classes = args.first
    else
      scope = args.first
    end
  else
    scope, classes = args
  end

  parallel = [Environment.cpu_count || 2, 2].min if parallel == true
  parallel = 0 if parallel == false || parallel.nil?

  scope ||= Shard.all
  if ::ActiveRecord::Relation === scope && scope.order_values.empty?
    scope = scope.order(::Arel.sql("database_server_id IS NOT NULL, database_server_id, id"))
  end

  if parallel > 1
    if ::ActiveRecord::Relation === 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).distinct
                              .filter_map(&:database_server).uniq
      # nothing to do
      return if database_servers.count.zero?

      scopes = database_servers.to_h do |server|
        [server, scope.merge(server.shards)]
      end
    else
      scopes = scope.group_by(&:database_server)
    end

    # clear connections prior to forking (no more queries will be executed in the parent,
    # and we want them gone so that we don't accidentally use them post-fork doing something
    # silly like dealloc'ing prepared statements)
    ::ActiveRecord::Base.clear_all_connections!

    parent_process_name = sanitized_process_title
    ret = ::Parallel.map(scopes, in_processes: (scopes.length > 1) ? parallel : 0) do |server, subscope|
      name = server.id
      last_description = name

      begin
        max_length = 128 - name.length - 3
        short_parent_name = parent_process_name[0..max_length] if max_length >= 0
        new_title = [short_parent_name, name].join(" ")
        Process.setproctitle(new_title)
        Switchman.config[:on_fork_proc]&.call
        with_each_shard(subscope, classes, exception: exception, output: :decorated) do
          last_description = Shard.current.description
          Parallel::ResultWrapper.new(yield)
        end
      rescue => e
        logger.error e.full_message
        Parallel::QuietExceptionWrapper.new(last_description, ::Parallel::ExceptionWrapper.new(e))
      end
    end.flatten

    errors = ret.select { |val| val.is_a?(Parallel::QuietExceptionWrapper) }
    unless errors.empty?
      raise errors.first.exception if errors.length == 1

      errors_desc = errors.map(&:name).sort.join(", ")
      raise Errors::ParallelShardExecError,
            "The following database server(s) did not finish processing cleanly: #{errors_desc}",
            cause: errors.first.exception
    end

    return ret.map(&:result)
  end

  classes ||= []

  result = []
  ex = nil
  old_stdout = $stdout
  old_stderr = $stderr
  scope.each do |shard|
    # shard references a database server that isn't configured in this environment
    next unless shard.database_server

    shard.activate(*classes) do
      if output == :decorated
        $stdout = Parallel::PrefixingIO.new(shard.description, $stdout)
        $stderr = Parallel::PrefixingIO.new(shard.description, $stderr)
      end

      result.concat Array.wrap(yield)
    rescue
      case exception
      when :ignore
        # ignore
      when :defer
        ex ||= $!
      when Proc
        exception.call
      # when :raise
      else
        raise
      end
    ensure
      $stdout = old_stdout
      $stderr = old_stderr
    end
  end
  raise ex if ex

  result
end

Instance Method Details

#_dump(_depth) ⇒ Object

custom serialization, since shard is self-referential



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# File 'lib/switchman/shard.rb', line 535

def _dump(_depth)
  id.to_s
end

#activate(*classes, &block) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 522

def activate(*classes, &block)
  shards = hashify_classes(classes)
  Shard.activate(shards, &block)
end

#activate!(*classes) ⇒ Object

for use from console ONLY



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# File 'lib/switchman/shard.rb', line 528

def activate!(*classes)
  shards = hashify_classes(classes)
  Shard.activate!(shards)
  nil
end

#database_server ⇒ Object 



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# File 'lib/switchman/shard.rb', line 496

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

#database_server=(database_server) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 500

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

#description ⇒ Object 



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# File 'lib/switchman/shard.rb', line 509

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

#destroy ⇒ Object 



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# File 'lib/switchman/shard.rb', line 594

def destroy
  raise("Cannot destroy the default shard") if default?

  super
end

#drop_database ⇒ Object 



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# File 'lib/switchman/shard.rb', line 543

def drop_database
  raise "Cannot drop the database of the default shard" if default?
  return unless read_attribute(:name)

  begin
    activate do
      self.class.drop_database(name)
    end
  rescue ::ActiveRecord::StatementInvalid => e
    logger.error "Drop failed: #{e}"
  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 'lib/switchman/shard.rb', line 581

def global_id_for(local_id)
  return nil unless local_id

  self.class.signed_id_operation(local_id) do |abs_id|
    abs_id + (id * IDS_PER_SHARD)
  end
end

#hash ⇒ Object

skip global_id.hash



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# File 'lib/switchman/shard.rb', line 590

def hash
  id.hash
end

#name ⇒ Object 



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# File 'lib/switchman/shard.rb', line 482

def name
  unless instance_variable_defined?(:@name)
    # protect against re-entrancy
    @name = nil
    @name = read_attribute(:name) || default_name
  end
  @name
end

#name=(name) ⇒ Object 



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# File 'lib/switchman/shard.rb', line 491

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

#original_id ⇒ Object 



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# File 'lib/switchman/shard.rb', line 518

def original_id
  id
end

#primary? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/switchman/shard.rb', line 505

def primary?
  self == database_server.primary_shard
end

#shard ⇒ Object

Shards are always on the default shard



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# File 'lib/switchman/shard.rb', line 514

def shard
  Shard.default
end