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
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 'app/models/switchman/shard.rb', line 612

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

.activate(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 96

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

.activate!(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 103

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

.categories ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 38

def categories
  CATEGORIES.keys
end

.clear_cache ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 137

def clear_cache
  cached_shards.clear
end

.current(category = :primary) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 92

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

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



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# File 'app/models/switchman/shard.rb', line 42

def default(reload_deprecated = false, reload: false, with_fallback: false)
  if reload_deprecated
    reload = reload_deprecated
    ::ActiveSupport::Deprecation.warn("positional reload parameter to Switchman::Shard.default is deprecated; use `reload: true`")
  end
  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
    if with_fallback && @default
      default = @default
    end

    # 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; rescue the fake default if the table doesn't exist
    @default = begin
      find_cached("default_shard") { Shard.where(default: true).take } || default
    rescue
      default
    end

    # rebuild current shard activations - it might have "another" default shard serialized there
    active_shards.replace(active_shards.dup.map do |category, shard|
      shard = Shard.lookup((!shard || shard.default?) ? 'default' : shard.id)
      [category, shard]
    end.to_h)

    activate!(primary: @default) if active_shards.empty?

    # 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
    if ::ActiveRecord::Base.connected? && ::ActiveRecord::Base.connection.shard.default?
      ::ActiveRecord::Base.connection.shard = @default
    end
  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 501

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 'app/models/switchman/shard.rb', line 432

def integral_id_for(any_id)
  if any_id.is_a?(::Arel::Nodes::Casted)
    any_id = any_id.val
  elsif any_id.is_a?(::Arel::Nodes::BindParam) && ::Rails.version >= "5.2"
    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
  else
    nil
  end
end

.local_id_for(any_id) ⇒ Object 



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

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 'app/models/switchman/shard.rb', line 117

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

  unless cached_shards.has_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 'app/models/switchman/shard.rb', line 384

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 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.wrap(yield objects) }
  end
end

.preload_cache ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 132

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 'app/models/switchman/shard.rb', line 480

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 'app/models/switchman/shard.rb', line 514

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

.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 492

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 'app/models/switchman/shard.rb', line 424

def signed_id_operation(input_id)
  sign = input_id < 0 ? -1 : 1
  output = yield input_id.abs
  output * sign
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. Note that parallel invocation currently uses
            forking, so should be used sparingly because you cannot get
            results back
:exception - :ignore, :raise, :defer (wait until the end and raise the first
            error), or a proc

Raises:

  • (ArgumentError) 


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# File 'app/models/switchman/shard.rb', line 152

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.wrap(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

  # back-compat
  options[:parallel] = options.delete(:max_procs) if options.key?(:max_procs)

  parallel = case options[:parallel]
               when true
                 [Environment.cpu_count || 2, 2].min
               when false, nil
                 1
               else
                 options[:parallel]
             end
  options.delete(:parallel)

  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.
          map(&:database_server).compact.uniq
      # nothing to do
      return if database_servers.count == 0

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

    exception_pipes = []
    pids = []
    out_fds = []
    err_fds = []
    pid_to_name_map = {}
    fd_to_name_map = {}
    errors = []

    wait_for_output = lambda do |out_fds, err_fds, fd_to_name_map|
      ready, _ = IO.select(out_fds + err_fds)
      ready.each do |fd|
        if fd.eof?
          fd.close
          out_fds.delete(fd)
          err_fds.delete(fd)
          next
        end
        line = fd.readline
        puts "#{fd_to_name_map[fd]}: #{line}"
      end
    end

    # only one process; don't bother forking
    if scopes.length == 1
      return with_each_shard(scopes.first.last, categories, options) { yield }
    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!

    scopes.each do |server, subscope|
      name = server.id

      exception_pipe = IO.pipe
      exception_pipes << exception_pipe
      pid, io_in, io_out, io_err = Open4.pfork4(lambda do
        begin
          Switchman.config[:on_fork_proc]&.call

          # set a pretty name for the process title, up to 128 characters
          # (we don't actually know the limit, depending on how the process
          # was started)
          # first, simplify the binary name by stripping directories,
          # then truncate arguments as necessary
          bin = File.basename($0)  # Process.argv0 doesn't work on Ruby 2.5 (https://bugs.ruby-lang.org/issues/15887)
          max_length = 128 - bin.length - name.length - 3
          args = ARGV.join(" ")
          if max_length >= 0
            args = args[0..max_length]
          end
          new_title = [bin, args, name].join(" ")
          Process.setproctitle(new_title)

          with_each_shard(subscope, categories, options) { yield }
          exception_pipe.last.close
        rescue Exception => e
          begin
            dumped = Marshal.dump(e)
            dumped = nil if dumped.length > 64 * 1024
          rescue
            dumped = nil
          end

          if dumped.nil?
            # couldn't dump the exception; create a copy with just
            # the message and the backtrace
            e2 = e.class.new(e.message)
            backtrace = e.backtrace
            # truncate excessively long backtraces
            if backtrace.length > 50
              backtrace = backtrace[0...25] + ['...'] + backtrace[-25..-1]
            end
            e2.set_backtrace(backtrace)
            e2.instance_variable_set(:@active_shards, e.instance_variable_get(:@active_shards))
            dumped = Marshal.dump(e2)
          end

          exception_pipe.last.set_encoding(dumped.encoding)
          exception_pipe.last.write(dumped)
          exception_pipe.last.flush
          exception_pipe.last.close
          exit! 1
        end
      end)
      exception_pipe.last.close
      pids << pid
      io_in.close # don't care about writing to stdin
      out_fds << io_out
      err_fds << io_err
      pid_to_name_map[pid] = name
      fd_to_name_map[io_out] = name
      fd_to_name_map[io_err] = name

      while pids.count >= parallel
        while out_fds.count >= parallel
          # wait for output if we've hit the parallel limit
          wait_for_output.call(out_fds, err_fds, fd_to_name_map)
        end
        # we've gotten all the output from one fd so wait for its child process to exit
        found_pid, status = Process.wait2
        pids.delete(found_pid)
        errors << pid_to_name_map[found_pid] if status.exitstatus != 0
      end
    end

    while out_fds.any? || err_fds.any?
      wait_for_output.call(out_fds, err_fds, fd_to_name_map)
    end
    pids.each do |pid|
      _, status = Process.waitpid2(pid)
      errors << pid_to_name_map[pid] if status.exitstatus != 0
    end

    # check for an exception; we only re-raise the first one
    exception_pipes.each do |exception_pipe|
      begin
        serialized_exception = exception_pipe.first.read
        next if serialized_exception.empty?
        exception = Marshal.load(serialized_exception)
        raise exception
      ensure
        exception_pipe.first.close
      end
    end

    unless errors.empty?
      raise ParallelShardExecError.new("The following subprocesses did not exit cleanly: #{errors.sort.join(", ")}")
    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 && !previous_shard.database_server.shareable?
      previous_shard.activate do
        ::GuardRail.activated_environments.each do |env|
          ::GuardRail.activate(env) do
            if ::ActiveRecord::Base.connected? && ::ActiveRecord::Base.connection.open_transactions == 0
              ::ActiveRecord::Base.connection_pool.current_pool.disconnect!
            end
          end
        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.wrap(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

#_dump(depth) ⇒ Object

custom serialization, since shard is self-referential



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# File 'app/models/switchman/shard.rb', line 608

def _dump(depth)
  self.id.to_s
end

#activate(*categories) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 593

def activate(*categories)
  shards = hashify_categories(categories)
  Shard.activate(shards) do
    yield
  end
end

#activate!(*categories) ⇒ Object

for use from console ONLY



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# File 'app/models/switchman/shard.rb', line 601

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 571

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 575

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 584

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

#destroy ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 675

def destroy
  raise("Cannot destroy the default shard") if self.default?
  super
end

#drop_database ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 616

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

  begin
    adapter = self.database_server.config[:adapter]
    sharding_config = Switchman.config || {}
    drop_statement = sharding_config[adapter]&.[](:drop_statement)
    drop_statement ||= sharding_config[:drop_statement]
    if drop_statement
      drop_statement = Array(drop_statement).dup.
          map { |statement| statement.gsub('%{name}', self.name) }
    end

    case adapter
      when 'mysql', 'mysql2'
        self.activate do
          ::GuardRail.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
          ::GuardRail.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
    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 663

def global_id_for(local_id)
  return nil unless local_id
  self.class.signed_id_operation(local_id) do |abs_id|
    abs_id + self.id * IDS_PER_SHARD
  end
end

#hash ⇒ Object

skip global_id.hash



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# File 'app/models/switchman/shard.rb', line 671

def hash
  id.hash
end

#name ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 557

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 'app/models/switchman/shard.rb', line 566

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

#primary? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'app/models/switchman/shard.rb', line 580

def primary?
  self == database_server.primary_shard
end

#shard ⇒ Object

Shards are always on the default shard



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# File 'app/models/switchman/shard.rb', line 589

def shard
  Shard.default
end