Class: Switchman::Shard

Inherits:
UnshardedRecord 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 616

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

.activate(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 65

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

.activate!(shards) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 75

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

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

    activated_classes << klass
    klass.connected_to_stack << { shard: shard.database_server.id.to_sym, klasses: [klass] }
    klass.connection_pool.shard_stack << shard
  end
  activated_classes
end

.clear_cache ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 106

def clear_cache
  cached_shards.clear
end

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



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

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

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



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# File 'app/models/switchman/shard.rb', line 26

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; 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

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

    # 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

.determine_max_procs(max_procs_input, parallel_input = 2) ⇒ Object

given the provided option, determines whether we need to (and whether it’s possible) to determine a reasonable default.



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# File 'app/models/switchman/shard.rb', line 485

def determine_max_procs(max_procs_input, parallel_input = 2)
  max_procs = nil
  if max_procs_input
    max_procs = max_procs_input.to_i
    max_procs = nil if max_procs.zero?
  else
    return 1 if parallel_input.nil? || parallel_input < 1

    cpus = Environment.cpu_count
    max_procs = cpus * parallel_input if cpus&.positive?
  end

  max_procs
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 462

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 389

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 'app/models/switchman/shard.rb', line 417

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 90

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 'app/models/switchman/shard.rb', line 341

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

.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 438

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 476

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 'app/models/switchman/shard.rb', line 22

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 'app/models/switchman/shard.rb', line 452

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 381

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, max_procs: nil, exception: :raise, &block) ⇒ 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 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
max_procs: - only run this many parallel processes at a time
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 121

def with_each_shard(*args, parallel: false, max_procs: nil, exception: :raise, &block)
  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 = 1 if parallel == true
  parallel = 0 if parallel == false || parallel.nil?

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

  if parallel.positive?
    max_procs = determine_max_procs(max_procs, parallel)
    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.zero?

      parallel = [(max_procs.to_f / database_servers.count).ceil, parallel].min if max_procs

      scopes = 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.to_h
    else
      scopes = scope.group_by(&:database_server)
      if parallel > 1
        parallel = [(max_procs.to_f / scopes.count).ceil, parallel].min if max_procs
        scopes = scopes.map do |(server, shards)|
          [server, shards.in_groups(parallel, false).compact]
        end.to_h
      else
        scopes = scopes.map { |(server, shards)| [server, [shards]] }.to_h
      end
    end

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

    wait_for_output = lambda do
      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 && parallel == 1
      return with_each_shard(scopes.first.last.first, classes, exception: exception,
                             &block)
    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, subscopes|
      subscopes.each_with_index do |subscope, idx|
        name = if subscopes.length > 1
                 "#{server.id} #{idx + 1}"
               else
                 server.id
               end

        exception_pipe = IO.pipe
        exception_pipes << exception_pipe
        pid, io_in, io_out, io_err = Open4.pfork4(lambda do
          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(' ')
          args = args[0..max_length] if max_length >= 0
          new_title = [bin, args, name].join(' ')
          Process.setproctitle(new_title)

          with_each_shard(subscope, classes, exception: exception, &block)
          exception_pipe.last.close
        rescue => e
          begin
            dumped = Marshal.dump(e)
          rescue
            # couldn't dump the exception; create a copy with just
            # the message and the backtrace
            e2 = e.class.new(e.message)
            e2.set_backtrace(e.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)
        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 max_procs && pids.count >= max_procs
          while max_procs && out_fds.count >= max_procs
            # wait for output if we've hit the max_procs limit
            wait_for_output.call
          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
    end

    wait_for_output.call while out_fds.any? || err_fds.any?
    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|
      serialized_exception = exception_pipe.first.read
      next if serialized_exception.empty?

      ex = Marshal.load(serialized_exception) # rubocop:disable Security/MarshalLoad
      raise ex
    ensure
      exception_pipe.first.close
    end

    unless errors.empty?
      raise ParallelShardExecError,
            "The following subprocesses did not exit cleanly: #{errors.sort.join(', ')}"
    end

    return
  end

  classes ||= []

  previous_shard = nil
  result = []
  ex = nil
  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
      result.concat Array.wrap(yield)
    rescue
      case exception
      when :ignore
        # ignore
      when :defer
        ex ||= $!
      when Proc
        exception.call
      # when :raise
      else
        raise
      end
    end
    previous_shard = shard
  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 'app/models/switchman/shard.rb', line 612

def _dump(_depth)
  id.to_s
end

#activate(*classes, &block) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 599

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 'app/models/switchman/shard.rb', line 605

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

#database_server ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 577

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

#database_server=(database_server) ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 581

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 590

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

#destroy ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 680

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

  super
end

#drop_database ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 620

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

  begin
    adapter = 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}', name) }
    end

    case adapter
    when 'mysql', 'mysql2'
      activate do
        ::GuardRail.activate(:deploy) do
          drop_statement ||= "DROP DATABASE #{name}"
          Array(drop_statement).each do |stmt|
            ::ActiveRecord::Base.connection.execute(stmt)
          end
        end
      end
    when 'postgresql'
      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 #{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 667

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 'app/models/switchman/shard.rb', line 676

def hash
  id.hash
end

#name ⇒ Object 



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# File 'app/models/switchman/shard.rb', line 563

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 572

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 586

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 595

def shard
  Shard.default
end